Shipping Container

ABSTRACT

The present invention relates to a shipping container for cryopreserved biological samples in which a cryopreserved sample can be maintained on arrival at its destination for a period of time, for example several months.

FIELD OF THE INVENTION

The present invention relates to a shipping container for cryopreservedsamples, for example biological samples, in which a cryopreserved samplecan be maintained on arrival at its destination for an extended periodof time, for example months, and can also possibly be used forcontrolled rate freezing and thawing. The containers of the inventioncould also be used for shipping other types of samples that requirecryogenic storage without the use of conventional cryogenic materialssuch as liquid nitrogen or solid carbon dioxide.

BACKGROUND TO THE INVENTION

Cryopreservation is a technique used for the preservation of biologicalsamples that involves cooling samples to, and maintaining them forprolonged periods at, very low temperatures, for example −78.5° C. to−196° C. By cooling a biological sample to a low temperature, thekinetics of chemical or enzymatic reactions that would otherwise degradethe sample are slowed to such an extent that the sample no longerdegrades or only degrades at a very slow rate. As a result, biologicalsamples can be stored over prolonged periods and then brought back toambient temperature as required for use and/or analysis.

Cryopreserved samples can be transported if their temperature ismaintained at a sufficiently low temperature during transit. If thesample is allowed to warm above a certain temperature, for example abovethe glass transition point of the sample, the integrity of the samplecan be compromised. This is because the cryoprotective agents used inthe cryopreservation process have a degree of toxicity towards thesample and more diffusion and therefore more chemical reactions canoccur which can affect the viability of the stored cells. Prolongedexposure to the cryoprotective agents and chemical reactions at highertemperatures and their cumulative effects causes damage to thecryopreserved material. Below the glass transition temperature theviscosity of the system means that cumulative effects are very small.During cryopreservation cooling from the cell's ambient temperatureneeds to be done in a controlled way to minimise damage and optimisecell viability post thaw. It is therefore evident that to ensure sampleintegrity in shipping the cryopreserved sample must be kept cold enoughfor the cumulative damaging effects not to be significant in theanticipated period of transportation and storage.

In addition to the need to maintain an adequately low temperature duringtransit the shipping container and its contents must be compatible withthe environments it passes through before, during and after transit.Thus, in the case of airfreight it is unacceptable on safety grounds fora phase transition coolant such as liquid nitrogen to be used if thereis a risk of spillage of the liquid nitrogen. To circumvent thisproblem, dry shippers, Dewar vessels with porous materials such asmolecular sieves or zeolites, have been developed to ensure that lowtemperature shipping can be achieved without the risk of liquid nitrogenspillage. In such Dewars liquid nitrogen is absorbed into the porousmaterial and is retained therein until it boils off as gaseous nitrogen.

A problem associated with these dry shippers is that the porousmaterials are easily contaminated, for example with particulatebiological material from the liquid nitrogen that remains in the dryshipper must be sterilised between each use and this makes their use insterile environments such as operating theatres and clean room highlyundesirable Additionally, the Dewar vessel is a vacuum jacketed vesseland to ensure equal pressure distribution on the vessel walls the shapeof the vessel must be approximately cylindrical or spherical as avoidingcatastrophic failure requires thicker materials and therefore poorerperforming Dewars. A combination of these factors means that the dryshippers are generally in the form of a cylindrical or spherical Dewarwith a relatively narrow aperture at one end through which charging withliquid nitrogen and sample occurs. A typical dry shipper has a bore thatprojects radially from the central axis of the Dewar's mouth. The porousmaterial in which the liquid nitrogen is absorbed is provided in thering between the outer wall of the bore and the innermost wall of theDewar and this dictates that the porous material (i.e. the molecularsieve element) cannot be removed and replaced easily and in any case notwithout first extracting the sample.

Simpler shipping containers containing a phase transition coolingmaterial such as solid carbon dioxide as the coolant (cryogen) can alsobe used for shipping cryopreserved samples and consist of an insulatedvessel, for example a Dewar or an insulated box, containing the sampleon or immersed in a bed of solid carbon dioxide. The problem with suchcontainers is that they are only capable of maintaining the sample at alow temperature for a relatively modest period of time and areunsuitable for shipping or storage over large time scale withoutfrequent recharging of the phase transition cooling material. Solidcarbon dioxide has a temperature of approximately −78.5° C. which isabove the glass transition temperature of many cryoprotective agents andthis temperature may not be low enough to prevent damage to the samplebefore, during, or after transport over longer timescales (days).

Developments in medicine mean that there is a growing need to ship andmaintain cryopreserved samples in environments where cryogenic materials(liquid nitrogen, solid carbon dioxide etc.) and storage facilities arenot available and/or practical. For example, the field of immunotherapyis rapidly developing and has significant potential for therapy, forexample in the treatment of cancers such as leukaemia and melanoma. Inone approach T-cells are harvested from a patient's blood and thengenetically engineered to introduce chimeric antigen receptors (CARs) ontheir surface. The resultant chimeric antigen receptor T-cells (CART-cells) are then grown up in the lab to provide a sufficient number fortherapy and are in turn transfused into the original patient. The CART-cells can then recognise the relevant protein antigen on the tumourcell's surface and in turn recruit the patient's immune system to killthose cells. This process requires the transfer of the blood and/ortissue samples to a laboratory capable of performing the geneticengineering thereon and then growing the requisite number of CART-cells. In addition, the CAR T-cells must then be shipped back to thepatient's own clinic and stored until the patient is ready fortreatment. This typically requires storage of the cryopreserved CART-cell sample(s) at the clinic for a period of several weeks or more andthis demands either construction of a local cryopreservation facility orprovision of a shipping container that can also serve as a storage uniton arrival. It is an object of the present invention to provide such ashipping container.

SUMMARY

In a first aspect the invention provides a shipping container forcryogenic samples comprising an insulated housing defining a cavity forreceiving a sample for cryopreservation and a thermal diode operable ina first state to provide cooling to the cavity and in a second state toimpair heat transfer into the cavity. In this aspect the cavity ispreferably suitable for receiving a replaceable cartridge of cryogenicphase transition material, in the case where a solid to liquid phasetransition cryogen is to be used a cartridge containing such a cryogenmay be fixably attached in the cavity.

In embodiments, the thermal diode is a gravitational thermal diode, i.e.a diode that operates under the influence of gravity and is capable ofmaintaining a temperature difference of up to 180° C. across itsvertical height with a power loss of less than 10 W, for example lessthan 5 W or less than 3 W. An advantage of having a gravitationalthermal diode is that in a state where no active cooling is provided tothe shipper the temperature differential between the base of the cavitycan be maintained solely under the influence of gravity. The thermaldiode may comprise an air blanket element and/or a closed circuitcondenser/evaporator loop element (thermosiphon). An advantage of theair blanket element is that the cost of the shipper is reduced. Anadvantage of the thermosiphon element is that cooling can beaccelerated. In embodiments, a heat engine is provided to remove heatfrom the thermal diode, in use the heat engine, for example a Stirlingcryocooler, will be thermally connected to a heat exchange element or athermosiphon or both so that heat can be removed from the cavity.Provision of a heat engine allows the temperature with in the shipper tobe brought to cryopreservation temperatures without the need for acryocoolant. The heat exchange element, when present, will be located atthe vertically uppermost portion of the cavity when the shippingcontainer is in an upright position and is preferably surrounded by aninfra-red shield.

In embodiments, the insulation element of the insulated housing maycomprise vacuum insulated panels. An advantage of vacuum insulatedpanels is their excellent insulating properties, relatively low cost andweight. Vacuum insulated panels can be easily formed into shapes noteasily accessible with Dewars, for example the cavity can besubstantially rectangular in cross section. The insulation element ofthe insulated housing may comprise a Dewar vessel. The insulationelement of the insulated housing may comprise a Dewar vessel and one ormore vacuum insulated panel, generally in this case the one or morevacuum insulated panel will be located outside the cavity defined by theDewar. An advantage of this construction is that excellent thermalperformance and resistance to failure of the Dewar is provided.

In embodiments, the shipping container may comprise one or more sensorsfor detecting the temperature within the cavity or the temperature of asample located in the cavity, the location of the container, the powerrequired to maintain the temperature within the cavity stable or theamount of cryogenic phase transition material in a cartridge located inthe cavity. An advantage of this is that the history of the samplepreservation conditions can be established and therefore the quality ofthe sample can be assured. The need for intervention to maintain sampleintegrity can also be determined.

Alternatively, or additionally, in embodiments the shipping containermay comprise an electronic contact for engagement with one or moresensors located within a replaceable cartridge of phase transitionmaterial. An advantage here is that monitoring of the cartridge can beperformed without opening the container, for example, remotely.

In embodiments, shipping containers equipped with sensors or configuredto receive sensor bearing cartridge of phase transition materialpreferably also a communication unit for reporting a reading from theone or more sensors. Remote monitoring of the conditions in the shippingcontainer is thus possible and alerts can be sent when intervention toensure sample integrity can be provided. The reading from the one ormore sensors in/on the container can indicate the position of theshipping container, the temperature in the cavity, the heat loss fromthe cavity, orientation of the cavity, shocks and vibration that thecavity has been exposed to or the integrity of the sample or acombination of such parameters.

Shipping containers according to embodiments also typically comprisingan insulated lid that is attachable to the container to seal the cavity.The lid may further comprise a lock, optionally wherein the lock isreleasable by remote control or by a remotely generated code, forexample in response to a signal verifying the integrity of thecryopreserved sample. Stored samples can thus be released to authorisedusers or when the integrity of the sample can be established through itspreservation history. Alternatively, or additionally, in embodiments thelid comprises a Stirling engine configured to remove heat from thethermal diode or is adapted to receive a Stirling engine configured toremove heat from the thermal diode. The shipping container can thus bemaintained at optimal temperature by powering up the heat pump, forexample a Stirling cryocooler from an internal or external power source.

In embodiments, the shipping container may comprise means for controlledrate freezing and/or controlled thawing. Such means may allow forcontrolling the descent of a sample into the cavity in response to areading from one or more sensors located in the cavity or on the sampleor the ascent of a sample up the cavity in response to a reading fromone or more sensors located in the cavity or on the sample, for examplea lift or winch arrangement. An advantage is that cryopreservation andsample thawing can be performed at locations where this would notusually be possible, for example in operating theatres withoutadditional equipment. In embodiments, extraction means for retrieving acryopreserved sample and/or replaceable cartridge of phase transitionmaterial from the cavity may also be provided to facilitate access to orremoval of the sample. In embodiments, the shipping container can insome embodiments comprise a conduit for fluid recharging of areplaceable cartridge of phase transition material located within thecavity of the container thus allowing recharging of cryogen withoutexposing the shipper cavity or sample to contamination. The shippingcontainer may be equipped with a replaceable cartridge for receiving acryogenic phase transition material. Advantageously the cryopreservationproperties of the shipper in offline, unpowered states, can bemaintained when such a cryogen containing cartridge is in place.

In a further aspect the invention provides a replaceable cartridge forreceiving a cryogenic phase transition material for use with a shippingcontainer as described above. The cartridge may comprise a handle thatextends towards the top of the thermal diode when installed in ashipping container. In advantageous configurations, the cartridge maycomprise one or more sensors for providing information on the fill stateor temperature of the cartridge and may be provided with a connector toform an electrical connection between the one or sensors in thecartridge and control electronics/communication unit.

In embodiments, the thermal diode is operable in a first state toprovide cooling to the cavity using a gas, and in a second state toimpair heat transfer into the cavity using a gas.

In a further aspect of the invention, there is provided a portablehousing for the shipping container described herein. The portablehousing may comprise an upper portion; a lower portion; and a drawermechanism slideably engaged with the lower portion. A shipping containerof the type described herein may be mountable in the drawer mechanism.

In a further aspect of the invention, there is provided a method forreducing a volume of liquid oxygen in a cavity of a shipping containerfor cryopreserved biological samples, the shipping container comprisinga first temperature sensor located near the top of the cavity, and asecond temperature sensor located near the bottom of the cavity, themethod comprising: measuring a first temperature at the top of thecavity; measuring a second temperature at the bottom of the cavity;determining a difference between the first temperature and the secondtemperature, wherein if the determined difference between the firsttemperature and the second temperature is within a specified range;switching on a heating mechanism to evaporate liquid oxygen in thecavity.

In a further aspect of the invention, there is provided a method forsafely switching-off an engine of a cryocooler, the method comprising:determining a mains power supply has been disconnected from the engine;sending a control signal to the engine to park; and de-coupling theengine from at least one battery

According to a related aspect of the present techniques, there isprovided a non-transitory data carrier carrying code which, whenimplemented on a processor, causes the processor to carry out any of themethods described herein.

As will be appreciated by one skilled in the art, embodiments of thepresent techniques may be embodied as a system, method or computerprogram product. Accordingly, present techniques may take the form of anentirely hardware embodiment, an entirely software embodiment, or anembodiment combining software and hardware aspects.

Furthermore, embodiments of the present techniques may take the form ofa computer program product embodied in a computer readable medium havingcomputer readable program code embodied thereon. The computer readablemedium may be a computer readable signal medium or a computer readablestorage medium. A computer readable medium may be, for example, but isnot limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing.

Computer program code for carrying out operations of the presenttechniques may be written in any combination of one or more programminglanguages, including object oriented programming languages andconventional procedural programming languages. Code components may beembodied as procedures, methods or the like, and may comprisesub-components which may take the form of instructions or sequences ofinstructions at any of the levels of abstraction, from the directmachine instructions of a native instruction set to high-level compiledor interpreted language constructs.

In a related aspect of the invention, there is provided a container forholding at least one cryopreserved biological sample within a shippingcontainer of the types described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The techniques are diagrammatically illustrated, by way of example, inthe accompanying drawings, in which:

FIG. 1 shows the basic structure of a shipper or shipping container withthe cryopreserved sample at the bottom of the Dewar and the Stirlingengine and heat exchanger at the top;

FIG. 2 shows the shipper of FIG. 1 with arrows to indicate theconvection circuit established when the Stirling engine is powered andthe thermal diode is in a first operational state;

FIG. 3 shows the temperature gradient across the thermal diode in theshipper in a second operational state wherein the Stirling cryocooler isunpowered and a temperature gradient is maintained under gravity by theinsulating air blanket in the cavity of the shipper;

FIG. 4A shows a condensing thermal diode element of the closed loop orgravity thermosyphon type, and FIG. 4B shows a shipping containercomprising the condensing thermal diode element of FIG. 4A;

FIG. 5 is a schematic showing the failure modes are associated withcryogenic shipping containers and how containers may be adapted to dealwith such failures;

FIG. 6 shows typical cell potency at different temperatures and wherethe shipper is designed to operate in normal and failure mode operation;

FIG. 7 shows a graph of temperature change over time in a shippingcontainer during cooling and warming, and a graph of cryocooler enginepower over time during cooling and warming;

FIG. 8 shows example steps performed by a system to reduce build-up ofliquified gas within a shipping container;

FIG. 9A shows a cross-sectional view through a shipping containercomprising a mechanism to reduce build-up of liquified gas within theshipping container, FIG. 9B shows a plan view of the mechanism, and FIG.9C shows a cross-sectional view of the mechanism;

FIG. 10A shows a cross-sectional view through a shipping containercomprising a mechanism to reduce build-up of liquid oxygen and frostwithin the shipping container, and FIG. 10B is a close-up view of themechanism;

FIG. 11A shows a cross-sectional view through a shipping containercomprising a thermal mass that surrounds a cryopreserved sample and ashield to reduce heat losses, FIG. 11B shows a plan view of the thermalmass, and FIG. 110 shows a cross-sectional view of the thermal mass;

FIG. 12 shows a cross-sectional view through a shipping containercomprising a thermal mass and an insulating plug;

FIG. 13 shows a cross-sectional view through a shipping containercomprising at least one getter;

FIG. 14A shows a view of a portable housing for housing a shippingcontainer, the portable housing comprising upper and lower portions,FIG. 14B shows a view of the portable housing with the upper portionraised, and FIG. 14C shows a view of the portable housing with the upperportion raised and the shipping container pulled-out;

FIG. 15A shows a cross-sectional view of a mechanism to raise and lowerthe upper portion of the portable housing of FIG. 14A, with the upperportion in a raised position; FIG. 15B shows the upper portion in alowered position; and FIG. 15C shows a mechanism to protect the shippingcontainer;

FIG. 16 shows a more detailed view of the portable housing and mechanismof FIG. 15A;

FIG. 17 shows a more detailed view of the upper portion of the portablehousing and mechanism of FIG. 15A;

FIG. 18A shows a container for holding a cryopreserved sample within ashipping container and for maintain the sample at a required temperaturewhen removed from the shipping container; FIG. 18B shows how acryopreserved sample is inserted into and extracted from the container;and FIG. 18C shows the structure of the container;

FIG. 19A shows a cross-sectional view through the container of FIG. 18A;

FIG. 19B shows how a graph of the rate of temperature increase of acryopreserved sample and elements of the container of FIG. 18A when thecontainer is removed from the shipping container;

FIG. 20A shows how elements of the container of FIG. 18A that enable thecontainer to be held within the shipping container; and FIG. 20B showshow the temperature of the cryopreserved sample within the container maybe monitored when the container is in situ;

FIGS. 21A to 21C show cross-sectional views through a shipping containerhaving an insulating plug and sealing mechanism;

FIG. 22 shows an example user interface of a portable housing for ashipping container;

FIG. 23 shows a schematic diagram of example steps to determine how longa shipping container may remain at a required temperature when thecryocooler is switched-off;

FIG. 24A shows a heat sink (or cool sink) of a shipping container; FIG.24B shows a cross-sectional view through an example heat sink having acircular form; and FIG. 24C shows a cross-sectional view through anexample heat sink having a rectangular form;

FIG. 25 shows a flow diagram of example steps to safely park a Stirlingengine of a cryocooler;

FIG. 26A shows a cross-sectional view through a shipping container andthe location of liquified gas build-up within the container, and FIG.26B shows a cross-sectional view through a shipping container comprisinga mechanism to reduce build-up of liquified gas within the shippingcontainer; and

FIG. 27 shows a cross-sectional view through a shipping containercomprising a mechanism for sterilising the shipping container.

DETAILED DESCRIPTION

Broadly speaking, the present techniques relate to shipping containers,and more particularly to portable shipping containers that may betransported from location to location by standard road, air and railfreight, and may be stored and used in conventional rooms, for exampleoperating theatres, at their destination. To ensure portability, it ispreferred that the shipping containers described herein are less than orequal to 1.5 m tall (i.e. have a height of ≤1.5 m).

In embodiments, the shipping containers may comprise an insulatedhousing, the housing defining a cavity for receiving i) a replaceablecartridge of phase transition material and ii) the sample to becryopreserved. The housing can be formed in any appropriate shape andfrom any appropriate material. In addition, the shipping containers maycharacteristically comprise a thermal diode operable in a first state toprovide cooling to the cavity and in a second state to impair heattransfer into the cavity. The thermal diode of the shipping containersmay be gravitational thermal diodes, i.e. thermal diodes that operateunder the influence of gravity, wherein gravity dictates that thevertically lowest portion of the cavity within the insulated housing ismaintained at a lower temperature than the other areas of the cavity.

FIG. 1 shows the basic structure of a shipper or shipping containercomprising an insulated housing 10. In FIG. 1, the housing 10 has acavity 12 defined by walls 14 a,b, a base 16 and a lid 18. The walls 14and base 16 can be a continuous structure such as a Dewar or a vacuuminsulated panel. An additional layer of insulated material and a hardshell can surround the walls and base though for clarity these are notshown. The lid 18 preferably comprises an insulant such as a vacuuminsulated panel or an expanded foam structure to minimise heat ingressinto the cavity 12. The housing can be enclosed in a further layer ofinsulation around the walls 14 and base 16, for example a layer ofvacuum insulated panels or a foamed insulation layer that additionallyprovides a degree of shock protection but for clarity these additionalinsulation elements are not shown. A surrounding hard shell can also beprovided. In addition, a removable cartridge of phase transitionmaterial will be installed in the cavity 12 and located towards its base22 but for clarity this is not shown in FIG. 1.

In FIG. 1, a sample 20 is provided towards the base 22 of the cavitythat is at the lower end of the thermal diode. (As explained withreference to FIGS. 9A to 9C, at least one shallow vessel may be providedat the base of the cavity, to collect liquified gas which forms at thetop of the cavity and drips down towards the base 22. The shallowvessel(s) may be considered to form a liquified gas reservoir). A heatexchanger 24, surrounded by an infra-red (IR) shield 26, is attached toa Stirling cryocooler 28 located on the lid 18. Alternative heat removalmeans such as a phase transition cryogen can be used in place of theStirling cryocooler. The IR shield mitigates any heat radiation from theheat exchanger 24 into the cavity 12 thus further improving the thermalperformance of the shipping container. In use the Stirling cryocooler ispowered to remove heat from the cavity 12 from the cavity's uppermostportion 30 that is also the uppermost portion of the thermal diode. Theshipper of FIG. 1 has a simple air blanket based thermal diode.

The thermal diode of the shipper of the invention works in twooperational states. In the first, active, state wherein the Stirlingcryocooler 28 is active heat is removed from the cavity 12 via the heatexchanger 24. As heat is removed from the cavity 12 a convection currentis established whereby the cooled air from the uppermost portion of thecavity 30 descends to the base 22 of the cavity. This may prevent orminimise the evaporation of liquid nitrogen (or other working fluid) andrecharge the system, as the liquid nitrogen drips from the heatexchanger 24 and into one of the shallow vessels (or liquid nitrogenreservoirs). An electromechanical control loop may stop the productionof liquid nitrogen when the system reaches its full state, where the“full state” is a predetermined volume and may depend on the liquifiedgas type, the thermal mass(es) used and the required standby time. Thisfull state may be a few millilitres if the build-up of liquified gas(e.g. oxygen) is undesirable. In this case, the nitrogen supply may befrom a nitrogen source e.g. a lab supply, a nitrogen concentrator, oroxygen scavenging system which uses air from the external environment asa source of working fluid for the cryocooler. At the same time anyrelatively hot air from the base of the cavity will rise towards the topof the thermal diode, i.e. the top of the cavity. This continuousconvection circuit allows constant heat extraction from the cavity andallows the lowermost portion of the cavity/thermal diode 22 to bebrought to a temperature suitable for cryopreservation, for example atemperature of −150° C. or less.

The heat flow/convection circuit established when the thermal diode isin the first, powered operational state is shown schematically in FIG. 2wherein operation of the Stirling cryocooler 28 causes heat to beremoved from the air located in the uppermost portion of the cavity 30via the heat exchanger 24. The cooled air descends to the base of thecavity 22 as indicated by arrows 32 while any relatively warm air willrise from the base of the cavity 22 to the uppermost portion of thecavity as indicated by arrows 34.

In the second, passive, state a temperature gradient is maintainedacross the gravitational thermal diode that relies on the insulationproperties of the housing 10 and the insulating properties of the airblanket in the cavity 10 (see FIG. 3). The lowermost portion 22 of thethermal diode is maintained at a temperature below that of the uppermostportion 30. The ratio of the cross-sectional area of the cavity to itsheight can be tailored to the desired operational performance. Forexample, a temperature difference of 220° C. can be obtained by using aheight to cross sectional area ratio of 75 cm:230 cm² with a heat lossof less than 1 W. This may enable a minimal heat gain in the system,which may advantageously enable the system to maximise the amount oftime for which the system is on standby, i.e. unpowered. This isparticularly useful in case of a power failure, or when the system isbeing transported over long distances (e.g. by plane).

FIG. 4A shows a condensing thermal diode element 38 of the closed loopor gravity thermosyphon type and FIG. 4B shows a shipping containeraccording to the invention fitted with such an element. In FIG. 4A a topcondensing chamber 40 is connected to a cold chamber 42, located at thebase of the closed loop, by a down pipe 44 and an up pipe 46 to form acontinuous circuit containing a working fluid such as nitrogen or argon.

The top condensing chamber 40 has a roof 48 formed with a with a lowestpoint vertically above a bowl 50 at the mouth of the down pipe 44 sothat, in the operational state in which heat is actively being extractedfrom the top condensing chamber by a heat pump (not shown), any workingfluid that condenses on the cooled roof drips down into the bowl 50 andthen down to the cold chamber 42 via the down pipe 44 under theinfluence of gravity. A reservoir of cold, liquid, working fluid 52 isthus established in the cold chamber 42. The build-up of condensedworking fluid in the cold chamber 42 drives any relatively warm workingfluid to migrate to the top condensing chamber via up pipe 46. An activecooling circuit is thus established when heat is being extracted fromthe top condensing chamber by a heat pump.

In the second operational state in which no active cooling is providedto the top condensing chamber a temperature gradient between the topcondensing chamber 40 and the cold chamber 42 is maintained undergravity as the coldest working fluid will reside at the verticallylowest point of the circuit and the warmest working fluid will rise tothe top of the circuit 40.

In embodiments, it may be beneficial to operate the shipping containersystem at an elevated pressure, such that the boiling point of theliquid nitrogen or other cryogenic liquid in the system is increased.This may enable the system to run at a lower cost and may provideimproved thermal efficiency, because of the lower temperaturedifferential within the system, and therefore, improved thermodynamicefficiency. In such embodiments, the closed system is initially chargedwith liquid nitrogen (or other working fluid). When the system hasequilibrated, the cryocooler is sealed and liquid nitrogen regenerationby/within the cryocooler may be initiated. This means that any liquidnitrogen which evaporates in the system is re-liquified by thecryocooler, such that the initial supply of liquid nitrogen can be usedand reused within the system. If any losses of liquid nitrogen occurfrom the system during prolonged operation, the nitrogen within theshipping container may be topped-up via an external supply. The shippingcontainer system may comprise a sensor to monitor liquid nitrogen (orother working fluid) levels within the container.

In an example closed shipping container system, the evaporated/gaseousnitrogen in the container is collected, re-liquified, and then returnedto the container for use in keeping samples at the required cooltemperature. For a shipping container with, for example, a 100 litreliquid nitrogen capacity, the liquid nitrogen evaporation may be lessthan two litres per day (when the system is in continuous operation).This evaporated nitrogen could be re-liquified with a cryocooler (e.g. aStirling cryocooler) having, for example, a 5 W to 20 W cooling capacityat 77K. Thus, the performance of the closed system may beenhanced/improved by using the cryocooler to reduce the temperature ofthe liquid nitrogen so that the amount of evaporation is reduced.

Thus, in embodiments, a cryocooler may be used to re-liquify liquidnitrogen in a closed system shipping container, to maintain the level ofcryogen within the shipping container. The cryocooler may be a Stirlingcryocooler, a Kleemenco cycle cryocooler, pulse tube cryocooler,“acoustic Stirling” cryocooler, Joule Thompson cryocooler or any othersuitable means of refrigeration.

In the insulated shipping container, the liquid nitrogen may exist asfree liquid or the liquid nitrogen may be adsorbed into an appropriatematerial. The shipping container may be vacuum insulated or insulated byany other suitable means.

In a closed shipping container system, when the nitrogen gas in a headspace of the cavity of the shipping container attains a particular state(for example, a particular pressure) it is taken to the cryocooler,which is operating at a temperature below the saturation temperature atthe pressure of the nitrogen gas (77K for liquefaction at 1 bar), toachieve liquefaction of the gas. The liquid is then returned to thecavity of the shipping container. The shipping container cavity has apressure relief valve in case of failure of the cryocooler, interruptionof power to the cryocooler, or failure of the insulation. When not beingemployed to liquefy nitrogen, the cryocooler may be used to reduce thetemperature of the liquid nitrogen in the closed cavity, and therebyreduce evaporation. The cold head of the cryocooler may be applieddirectly to the liquid nitrogen within its insulated pressure vessel.Alternatively, a thermosiphon or any other appropriate system may beused to facilitate heat transfer between the liquid nitrogen and thecryocooler.

An advantage of recycling the liquid nitrogen within the shippingcontainer is that the cost of operating the shipping container isreduced, as liquid nitrogen is expensive and may not be readilyavailable everywhere. Another advantage is that the need to store andhandle large volumes of liquid nitrogen is reduced, which reduces theamount of training and safety processes required to use the shippingcontainer. Another advantage is that the liquid nitrogen that isrecycled contains low levels of contaminants.

FIG. 6 shows typical cell potency at different temperatures and wherethe shipper is designed to operate in normal and failure mode operation.It can thus be appreciated that even in failure mode operation theshippers according to the present invention are capable of maintainingcryopreserved samples at temperature at which the integrity of thesample is not compromised for a period of days or weeks.

In embodiments, the gravitational thermal diodes of the shippingcontainers may operate in two states. In a first operational state, heatmay be actively extracted from the thermal diode through heat exchangefrom inside the cavity to the exterior of the shipping container. Inthis state, a cooling circuit is established with heat being removedfrom working fluid located at the vertically uppermost part of thecavity, the cooled working fluid then descends to the verticallylowermost portion of the cavity while any relatively warm working fluidrises to the vertically uppermost portion of the cavity. In this firstoperational state, the cavity is cooled to establish or maintain atemperature suitable for cryopreservation. The temperature at thevertically lowermost portion of the cavity can be brought totemperatures below the phase transition temperature of a phasetransition material contained with a cartridge located therein. Forexample, a cartridge containing solid carbon dioxide may be placed atthe base of the cavity along with a sample for cryopreservation and thevertically lowermost portion of the cavity can be cooled to temperatureof −150° C. or below whilst the transition temperature of solid carbondioxide to gas is −78.5° C. The cartridge of phase transition materialcan be inserted via an opening at the top of the cavity withoutdisturbing the integrity of walls, floor or opening of the cavity. Thereplaceable cartridge may be fixably attached to the walls and/or floorof the cavity and can define a location, e.g. a slot, niche or wellindependently or in conjunction with the walls and floor of theinsulated housing. The working fluid of the thermal diode may becontained in a closed loop or may be in the form of a simple airblanket. In order to operate the thermal diode in this first operationalstate a heat pump or an alternative cooling means such as liquidnitrogen is typically coupled to a heat exchanger located within thecavity defined by the insulated housing in use.

In a second operational state, the thermal diode operates to maintainthe vertically lowermost portion of the cavity of the shipping containerat a lower temperature than the vertically uppermost portion of thecavity. This relies on gravity maintaining a thermal gradient across thecavity wherein the coolest air and/or working fluid resides at thevertically lowermost portion of the cavity. Details of specific thermaldiodes that may be used in embodiments of the shipping containers areprovided herein.

In embodiments, the shipping containers may be capable of maintaining asample at a temperature of −78.5° C. or less than −150° C. or below fora prolonged period of time, for example many weeks to many months withpower applied. Without external power being applied, e.g. when no poweris provided to a Stirling cryocooler or similar heat engine,temperatures in the container can be maintained from 2 hours to up toweeks. The thermal diodes may be capable of maintaining a temperaturedifference between the vertically lowermost point of the cavity and thevertically uppermost portion of the cavity of from 20° C. to 150° C.,for example 80° C., 100° C. or 120° C. or more. The ratio of the crosssectional area of the cavity to its height can be tailored to thedesired operational performance. For example, a temperature differenceof 220° C. can be obtained by using a height to cross sectional arearatio of 75 cm to 230 cm² with a heat loss of less than 1 W. Thediameter of the system is optimally wide enough for bags ofcryopreserved therapy to be inserted (typically these bags are less than160 mm wide) which is also wide enough to allow adequate convectionwithin the cavity.

In embodiments, the shipping containers may have a maximum power loss ofless than 10 W depending on cavity size and temperature difference fromthe top to the bottom of the cavity. In preferred embodiments, the powerloss from the shipping container is less than 5 W and most preferablyless than or equal to 3 W.

The insulated housing may have an opening at the top of the cavitythrough which a sample, for example a biological sample, forcryopreservation and a replaceable cartridge of phase transitionmaterial can be loaded. In use the shipping container may be fitted witha lid that covers the cavity in the housing. The lid serves to close thecavity to protect the contents of the cavity from contamination andprovides insulation to the top of the container thus preventing orsubstantially reducing ingress of heat into the container into thecavity. The lid typically comprises an insulating element made from anysuitable insulated material such as vacuum insulated panels as discussedherein, an insulating foam or the like. The lid can also comprise a hardshell material to protect the container from impact damage, the shellcan be made from any convenient material such as a plastics material, acomposite material, a metal or metal alloy with selection being made onthe balance of weight and strength requirements.

The insulated housing may, for example, be a Dewar vessel, i.e. a vesselwith a vacuum jacket with said vacuum providing for very low thermalconductivity and thus good insulating properties. The use of Dewarvessel does provide some design limitations as the need to balancepressure on the walls of a Dewar usually dictates that such vessels aresubstantially spherical or cylindrical in section (as otherwise muchthicker wall sections will be required to withstand atmosphericpressure) and typically have an opening (through which e.g. a sample anda user replaceable phase transition cryogen cartridge can be introduced)that is often much narrower (of smaller cross section) than the internalcavity of the Dewar vessel and this restricts the size and shape ofsample and the user replaceable cartridge of phase transition material.To modify the shape of a Dewar much thicker walls sections are requiredand such vessels are heavier, more difficult to construct and thermalperformance of the Dewar may deteriorate. Nonetheless Dewar vesselsgenerally have excellent insulation properties.

In some preferred examples, the insulated housing may be formed fromvacuum insulated panels (VIPs), for example the vacuum insulated panelssupplied by Kevothermal (www.kevothermal.eu) and related panels of thistype such as Kingspan OPIM-R®. In general terms, the VIP features amicroporous core that is evacuated and then encased and sealed in a thingas tight envelope. Kevothermal VIPs are made from an amorphous silicabased low thermal conductivity core, with added infra-red opacifiers,encased in a multi-layered metallised barrier film, giving thermalconductivity as low as 0.0036 W/m/K as measured according to ASTM C518,EN 12667 in the centre of panel. The insulating properties of the VIPscompares very favourably with insulants such as expanded polyurethanefoam, expanded polystyrene and fibre glass insulation that have thermalconductivities in the region of 0.025 W/m/K, 0.034 W/m/K and 0.05 W/m/Krespectively. A plurality of VIPs can be combined in a laminatestructure to deliver sufficient insulation to the container.

Vacuum insulated panels are advantageously relatively inexpensive. VIPscan also be easily formed into any convenient shape as there is no needto balance pressure as is the case for Dewar vessels. Thus, thecross-section of the cavity can continue through to the opening ofhousing and may be shaped in any suitable shape for receiving a sampleand a replaceable cartridge of phase transition material. For example,the cavity can be square or rectangular in cross section renderinginsertion of sample and replaceable cooling cartridge facile. VIPs arealso much more robust against damage that than Dewar vessels and, ifdamaged, the VIPs forming the walls of the housing can be replaced torepair the container.

It has also been found that the insulating properties of the insulatedhousings of shipping containers comprising vacuum insulated panels(VIPs) are superior to the insulating properties provided by manyconventional Dewar vessels in certain temperature ranges, notably in therange of temperatures greater than −78° C. As a result, cooling of thesample containing cavity of a shipping container constructed from VIPscan advantageously be achieved with a Stirling cryocooler of lowercapacity than that that would be required to cool a shipping containerwith a conventional Dewar of the same volume. This is advantageous interms of cost of goods and, commonly, in terms of container weight asthe lower capacity pumps are usually lighter than higher capacity pumps.Furthermore, cryocoolers operating down to −100 to −120° C. areconsiderably less expensive than those operating to −196° C.

This variation in thermal performance of conventional Dewars across therange from room temperature to −196° C. stems from the fact thatconventional Dewar vessels for cryopreservation are principally designedto operate at liquid nitrogen temperature and are directly cooled tothat temperature with liquid nitrogen. As a result, the insulatingproperties of the Dewar across the temperature range from liquidnitrogen temperatures to room temperature are less important designcriteria than the ultimate insulation properties at liquid nitrogentemperatures (−196° C.). The interior of a Dewar vessel's vacuum jacketis partially coated with a getter material that, at low temperatures,serves to absorb any residual gas within the vacuum jacket therebyimproving the vacuum and thereby reduce the thermal conductivity of theDewar (i.e. improve the insulating properties of the vessel). Thiseffect is known as the cryopumping effect. The inventors of the presentinvention identified that this cryopumping effect often only worksefficiently at temperatures below the temperatures convenient for theshipping containing application wherein cooling is performed in situ bya heat pump. The result of the cryopumping effect in conventional Dewarsonly working at reduced pressures is that the effective thermalconductivity of the Dewar is higher than that of a vessel formed fromVIPs at temperature greater than approximately −80° C. To avoid thisproblem with conventional Dewars, modified Dewar vessels withadvantageous and better heat loss properties at higher temperatures thatcomprise new types of getters (e.g. charcoal) have been developed. As aresult of using this new type of getter materials, Dewar vessels havebeen developed that function well across the targeted operationtemperature range of the shipping containers.

At present VIPs are provided as flat panels and can be combined aslaminates to form the walls and floor of the shipping container. Whilethis construction provides excellent insulation properties the flatpanel nature of the VIPs means that where the panels meet at an anglethere is a potential path for heat ingress. To address this issue it isenvisaged that a VIP can be formed as a box with an opening, or othersuitable shape for use as an insulated housing in the shippingcontainers of the invention. Thus the invention provides a method forforming an insulated structure comprising the steps of forming amicroporous core with a floor and at least one wall projecting upwardstherefrom such that a cavity between the wall and floor is produced,evacuating said core under reduced pressure, and then sealably encasingthe core in a thin gas tight envelope. The invention also relates to aninsulated structure with a floor and at least one wall projectingupwards therefrom defining a cavity between the floor and the at leastone wall comprising a continuous microporous core held under reducedpressure in a gas tight envelope. It is preferred that the gas tightenvelope encasing the microporous core comprises a foil element toreduce radiative heat transfer thus further improving the insulatingproperties of the housing.

In some embodiments the shipper structure combines an insulated housingcomprising Dewar vessel and a vacuum insulated panel. This particularstructure is advantageous because a common failure mode for Dewars isfailure through loss of vacuum in the Dewar vacuum jacket. If Dewarfailure occurs in a conventional Dewar cryoshipper, the temperaturewithin the Dewar vessel can rise rapidly since the thermal conductivityof the Dewar can increase by a factor of 10 or more and compromise theintegrity of a cryopreserved sample contained within that Dewar vessel.It is thus advantageous to provide an additional, secondary, layer ofinsulation to the shipper outside the Dewar vessel that, in the instancewhere the Dewar vessel vacuum fails, provides sufficient insulation tomaintain an acceptably low temperature to maintain sample integrity. Ashipper structure in which the insulated housing comprises a Dewarvessel surrounded by VIPs that advantageously allows an adequate windowof time for transfer of a cryopreserved sample to a replacementvessel/shipper should the Dewar vacuum fail is thus provided by thepresent invention.

It has been found that use of VIPs of a cross sectional thickness ofcirca 50 mm around a Dewar vessel is sufficient to keep power loss fromthe sample cavity of the shipper to less than 30 W at −78.5° C. (in theevent that the vacuum in the Dewar vessel fails). The thickness of theVIPs providing the back-up insulation can be varied to meet the targetthermal performance criteria and to satisfy any applicable weightrequirements. In practical terms, this secondary insulation allows analarm to be raised and an adequate window of opportunity to transfer thesample to an alternative shipper or static storage container that wouldnot be available with a standard Dewar cryoshipper. With this dualDewar/VIP insulated housing structure a cryopreserved sample at the baseof the cavity of the shipping container can be maintained in the targetoperational range for up to approximately 2 days in the event that theDewar vacuum fails.

The VIPs that surround the walls of the Dewar can be formed in acomplementary shape to the outer walls of the Dewar vessel so thatoptimal thermal contact is maintained between the VIP and the Dewar. Insome preferred embodiments the insulating layer outside the Dewar vesselcan be formed from a plurality of VIPs. For example, in the case wherethe Dewar is of circular cross section about its vertical axis, two,three, four or more VIPs of complementary arcuate cross section can beprovided so that the cross section of the entire circumference of thecurved outer wall of the Dewar vessel is insulated by a complementaryarcuate VIP. Alternatively, flat VIPs may be used to form a box in whichthe Dewar resides and any voids between the inner wall of the VIP andthe outer wall of the Dewar may be filled with a further insulant, forexample a foamed insulant that may also cushion the Dewar againstexternal shock. Advantageously, the shipper can be constructed to allowrepair by replacement of any failed Dewar unit or VIP element in thestructure.

The insulated housing typically has an outer shell to protect thehousing from impact damage. The cavity of the housing, or the shippingcontainer as a whole, may be lined with a material that can besterilised under standard conditions such as, but not limited to, steamsterilisation, chemical sterilisation, such as hydrogen peroxide vapoursterilisation, radiation sterilisation, and high temperaturesterilisation e.g. and autoclave. Exemplary materials for the shell orthe cavity lining may be selected from metals, metal alloys, ceramics,glasses, laminates for example glass or carbon fibre based laminates,resins or polymers. Strong, lightweight materials are particularlypreferred as these minimise the total weight of the container.

The lid and/or housing may also comprise other functional components.The other functional components as described below may be provided forindividually or in combination. For example, the lid and/or housingpreferably comprises a heat exchanger that is provided with means forcoupling to a heat pump such as a Stirling cryocooler (sometimesreferred to herein as a Stirling engine) or a reservoir for receiving acryogen such as liquid nitrogen so that heat can be extracted from thecavity to effect cooling of the cavity when the thermal diode isoperated in its first operational state. In this case a Stirlingcryocooler can be incorporated into the lid of the shipping container orattached to the insulated housing so long as it is in thermal contactwith the heat exchanger. In cases where the heat exchanger is present itis preferred that the heat exchanger is surrounded by an infra-red (IR)shield to prevent heat radiating from the heat exchanger back into thecavity. The IR shield in this case can comprise a simple metallic foil.

An electrically powered means of driving heat extraction from the cavityof the shipping container is generally preferred as this reducesreliance on external sources of cryogens that are not readily availablein all locations. It will thus be understood that in preferredembodiments described herein and above either the lid or housing may beequipped with a Stirling cryocooler configured to cool the cavity whenthe lid is located on the housing and when the Stirling cryocooler ispowered.

The lid or body may also provide a display to indicate the temperatureof, for example, the sample, a portion of the cavity or the cartridge,the fill level of the cartridge or other information relating to thestatus of the contents of the container, for example whether the samplehas been maintained at the appropriate temperature since the sample wasintroduced. The status indications will be derived from readingsobtained from sensors located within the cavity, in or on the sample, inor on the replaceable phase transition cartridge or in a combination ofthese locations. The lid and or housing may comprise a location sensor,for example a GPS sensor so that the location of the container may betracked and verified remotely. Also as the thermal diodes of the presentinvention are gravitational thermal diodes it is important that theshipping container is maintained in an upright state and so the lidand/or housing may be equipped with a tilt sensor to ensure that theshipping container is maintained in an upright position. A sensor canalso be provided to provide a report on the power required to maintainthe temperature within the cavity at a constant temperature and this inturn can be used to determine whether the insulation is intact, forexample whether a Dewar vessel has failed or not. A sensor may alsoreport on the operational state of any heat engine, or the remainingpower of any on board power source that might be present, for example topower a heat pump or a communication unit.

The housing may also be equipped with a locking means to engage withcomplementary locking means on the lid. For example, the shippingcontainer may be provided with a manual or electronic lock. Opening ofthe lock and/or lid may trigger a report from sensor to a remote node orto a display on the shipping container to allow monitoring of samplestatus and the handling of a cryopreserved material in compliance with aprotocol, such as a regulatory protocol for material to be used in atherapeutic or non-therapeutic intervention.

In some embodiments the lid and or housing will comprise communicationmeans for reporting the status of the shipping container and itscontents to a remote server or node. The information that is reportedmay for example be the fill status of the cartridge and/or thetemperature of the container. The report may trigger dispatch of areplacement replaceable cartridge to replace that already installed inthe shipping container to ensure continuity of cryopreservation. Sensorreadings on the condition of the sample or container can likewise bereported to a remote node to ensure that any necessary user interventionis reported in a timely manner. The communication means can communicatewith a remote server via standard protocols such as Wi-Fi, Bluetooth®,GSM or satellite messenger modules. The communication means can also beconfigured to receive information from a remote server, for example toallow the shipping container to be released to an end user when it isdetermined that the sample has been maintained under the appropriateconditions.

The housing or lid may also be provided with a connector adapted forintroducing cryogen into a cartridge located in the cavity defined bythe insulated housing wherein said connector is in use in sealable fluidconnection with that cartridge. This configuration advantageously allowsfor introduction of phase transition cryogen without opening theshipping container thus avoiding risking introducing contamination intothe container or triggering heat loss therefrom. In such configurations,the connector will be provided with venting means to avoid excessivebuild-up of pressure.

The thermal diode of embodiments of the present invention may beoperable in a first state to provide cooling to the cavity and in asecond state to impair heat transfer into the cavity. The thermal diodesof the shipping containers may be gravitational thermal diodes. Agravitational thermal diode requires that the diode is maintained in anupright position in order to maintain a temperature gradient between itsvertically uppermost and lowermost extremities. As will be evident tothose skilled in the art heat will rise from the lowest end of the diodeto its upper end thus establishing a thermal gradient across the diode.Thus, the coldest zone of the thermal diode and by extension the cavityin the shipping container is located at the vertically lowest end of thethermal diode and the warmest zone of the thermal diode. For theavoidance of confusion, the discussion of the thermal diode herein andabove refers to the elements of the thermal diode by their position whenin use, thus reference to top and bottom elements, upper and lowerelement refer to the elements that are located at e.g. the top of thedevice when in use.

The inventors have discovered that in its simplest form the thermaldiode can be a simple blanket/circulation of gaseous working fluid, forexample air, located above the sample and the opening located at the topof the cavity provided that the ratio of the cross sectional area aroundthe vertical axis of the cavity and the vertical height of the diodesection is of an appropriate minimum value. The present inventors havefound that the power loss associated with using an air blanket as athermal diode can be 3 W or less, for example 1 W or less, withouthaving an excessively or impracticably high cavity that would prohibitmanual loading of sample and cartridge or render transport and storagein conventional vehicles and rooms impossible. The air blanket thermaldiode according to the invention thus operates in a passive state tominimise heat ingress into the cavity by exploiting the low thermalconductivity of air. It is necessary to maintain the air blanket thermaldiode in an upright state as otherwise the equilibrated insulatingblanket of air can be disturbed and this would lead to increased heatingress into the cavity.

In order to receive a reasonable amount of sample a replaceablecartridge of phase transition cryogen the cross sectional area of thecavity is typically in the range of 150 cm² to 2000 cm². The ratio ofthe cross sectional area of the cavity in cm² to the height of thethermal diode in cm is typically greater than 1:2 and preferably 1:3 ormore. For example, an insulated housing with a heat loss of 1 W of crosssectional area of 230 cm² and a height of 75 cm can maintain atemperature difference across the thermal diode of 220° C. Routinecalculations can be used to determine the aspect ratio (height to crosssectional area) of a thermal diode based on the thermal power loss fromthe cavity and the target temperature differential across the thermaldiode. For example, shipping containers designed to maintain a greatertemperature differential will have a greater aspect ratio (i.e. theratio height:cross sectional area).

The air blanket/circulation thermal diode, and indeed the othergravitational thermal diodes according to the invention can operate topositively cool the sample when cooling means are applied at theuppermost portion of the thermal diode. This advantageously allows thesection of the shipping container to be cooled without changing thereplaceable cartridge containing phase transition material. In addition,in the instance where the phase transition material contained with thereplaceable cartridge is a material that undergoes a solid to liquidphase transition the cartridge can be regenerated by application ofcooling means to the thermal diode. For cartridges containing otherphase transition material, i.e. solid to gas or liquid to gas phasetransition materials the application of cooling means to the thermaldiode arrests the phase or substantially reduces the rate of the phasetransition and substantial maintains the cooling capacity of thecartridge.

In some cases, the cooling means for the thermal diode comprises aStirling cryocooler. Stirling cryocoolers are devices that convertmechanical energy into heat energy that can be conveniently driven underelectrical power. To improve the efficiency of heat transfer from thecavity defined by the insulated housing the Stirling cryocooler ispreferably attached to a heat sink. The heat sink provides a largeinterfacial surface area over which heat from the gas in the air blanketthermal diode can be extracted. The relative density of cooled airensures that the cooled air sinks to the base of the blanket while lessdense warmer air rises to the top of the blanket thus establishing acyclical cooling current in the air blanket thermal diode when coolingmeans are applied to the diode. The heat sink is preferably locatedtowards the uppermost section of the thermal diode, for example at thetop of the cavity defined by the insulated walls of the housing. Theheat sink can be attached to the insulated wall sections of the housingor to the lid of the container. The Stirling cryocooler itself can belocated in the lid of the shipping container or can be engaged with thelid or the housing so that it is in thermal contact with the thermaldiode, optionally via an intermediate heat exchanger that is integratedto the lid, the housing or the Stirling engine.

The cooling means provided to the thermal diode can also be phasetransition cooling means. Thus a cryogen such as liquid nitrogen orsolid carbon dioxide can be coupled to a heat exchanger to extract heatfrom the top of the thermal diode. The charge of cryogen used to operatethe thermal diode can be conveniently provided in a user replaceablecartridge adapted for this purpose or from a liquefied gas or gascylinder such as carbon dioxide which is then used to produce a solid orliquid medium as the refrigerant using the Joule-Thompson effect.

Any heat exchanger present can be provided with an infra-red reflectivefoil surround or shroud. This shroud can be a multilayer insulating foiland advantageously prevents radiation of heat into the cavity whencooling is not supplied to the thermal diode. The shroud has at leastone aperture to allow air flow to and from the heat exchanger.

In some embodiments the thermal diode is a thermal diode of the closedcircuit condenser/evaporator type, for example a thermal diodecomprising a thermosiphon. A closed circuit condenser/evaporator thermaldiode comprises a closed loop containing a working fluid. It ispreferred that the working fluid in the loop is a gas that liquefies ata temperature between −100° C. and −200° C. Preferred working fluids arenitrogen and argon. It is preferred that the pressure of the workingfluid is not greater than 200 bar at room temperature and a volume of 1litre, thus avoiding significant complications with regulations forcontainment of pressurised vessels. The closed circuit typically has theform of two chambers in fluid communication, an upper chamber and alower chamber, connected by a plurality, for example two, thin walledpipes. The pipes are thin walled pipes to minimise thermal conductionvia the pipe walls from the top end of the thermal diode to the bottomend of the diode. The pipes are also of a relatively small wall crosssection, this provides for a better temperature gradient across thethermal diode and improved circulation of working fluid within thecircuit. The lower chamber in both operational states absorbs heatenergy from the base of the cavity into the working fluid causing thatworking fluid to rise through the pipe into the upper chamber. Heatenergy can then be transferred from the working fluid located in theupper chamber via a heat exchanger. Condensation of working fluid occursin the upper chamber of the closed loop, for example on the cooled innerroof of the upper chamber.

In an advantageous arrangement for the closed circuitcondenser/evaporator thermal diode, the roof of the upper chamber slopesdownward to a lowest point to which condensate will gravitate and fallfrom in drips. In the floor of the chamber below this point in the roofis located a first pipe linking the upper and lower chambers, the entryto said first pipe is located at the lowest point of the floor of theupper chamber. A second pipe linking the upper chamber and the lowerchamber terminates at a point in the floor of the upper chamber, theentry to the second pipe in the floor of the upper chamber is verticallyabove the entry to the first pipe. The condensation and dripping processfavours rapid flow of condensate to the lower chamber through one tubepreferentially. Such a system can have a vertical height of 0.2 mupwards although typically the systems have a height of circa 0.7 m. Thecircuit volume can be vary depending on the cooling power required butin the systems tested this was relatively small at approximately 50 ml.FIG. 4A shows this arrangement of thermal diode. In practice thesesystems are operated at raised pressure (typically less than thesupercritical pressure of the fluid or 200 bar for safety reasons atroom temperature) with nitrogen or argon gas with can produce a heatpipe with a difference in temperature of thermal gradients in the rangeof approximately 1° C. per Watt of cooling power delivered. Whilst argonis advantageous due to its higher boiling point (thus starting the gasto liquid heat exchange cycle at warmer temperatures) when runningsystems to low temperatures (less than −180° C.) which require highcooling powers greater than approximately 10 W then the argon can freezeand stop the liquid flow through the system thus causing the thermaldiode to stop functioning. In these situations, due to its lowerfreezing point nitrogen is preferred.

The gravitational thermal diode of the closed circuitcondenser/evaporator type (also referred to as a gravity thermosiphontype thermal diode) can operate in two states. In a first, activelycooled operational state, the heat is extracted from the upper chamberof the thermal diode by active cooling that is provided by coolingmeans, for example by a Stirling cryocooler in thermal contact with theupper chamber or through cooling with a phase transition cryogenthermally coupled to the upper chamber as described above for the airblanket thermal diode. The active cooling causes the working fluid tocondense and the liquid, that has a higher density than gaseous workingfluid descends to the lower chamber via a pipe in the closed circuitunder the action of gravity. Heat absorbed by the lower chamber isconducted into the liquid working fluid causing evaporation of theworking fluid. The heated gaseous working fluid then rises up into theupper chamber wherein it condenses under the action of the activecooling to complete the cooling circuit. In a second state agravitational cooling cycle based on the rise and fall of the gaseousworking fluid that is dictated by the relative density of the workingfluid that increases as the temperature of the working fluid decreases.

The cavity of the shipping container according to the invention isadapted to receive a replaceable cartridge of cryogenic phase transitionmaterial. As used herein and above, a cryogenic phase transitionmaterial is a material that undergoes a phase transition at atemperature of −78° C. or below. In use and in some embodiments theshipping container comprises a replaceable cartridge for receiving aphase transition material or containing a phase transition material. Thephase transition material to be received in the replaceable cartridge orcontained therein is selected so that it undergoes a phase transition ata temperature that is sufficiently low for preservation of acryopreserved sample for a prolonged period of time, typically thistemperature is below the glass transition temperature of the sample, forexample a temperature below −70° C. Preferred examples of phasetransition materials are liquid to gas phase transition material such asliquid nitrogen which undergoes a liquid to gas phase transition at−196° C., solid to gas phase transition materials such as solid carbondioxide which undergoes a solid to gas transition at −78° C. and solidto liquid phase transition materials such as solid ethanol thatundergoes a solid to liquid phase transition at −114° C. Other solid toliquid phase transition material are well known in the art and includedimethyl sulfoxide (DMSO), salt (NaCl) and water mixtures, for examplein the weight ratio of 62:5.56:38.44. In some cases, it is preferable touse a phase transition material that does not transition into a gas asthis avoids the need to provide venting of the gas that is generated bythe phase transition. It can also be advantageous to use a materialsolid to liquid phase transition material such as ethanol as the coolingcapacity of the cartridge can be regenerated by cooling of the cartridgein situ, for example by operating the thermal diode comprised by thecontainer with cooling means, for example cooling the thermal diode witha Stirling cryocooler or by direct introduction of a cryogen onto thecartridge surface to solidify any liquid phase transition material thathas formed within the cartridge. If direct refreezing is to be performedit is preferable to remove the cartridge from the shipper toavoid/minimise contamination.

The invention also relates to the user replaceable cartridges that areadapted to fit within the shipping containers according to theinvention. The invention also relates to shipping containers asdescribed herein that are fitted with a replaceable cartridge asdescribed herein and above. The replaceable cartridges or cartridgescomprise a housing in which the solid or liquid phase transitionmaterial is received or contained. The phase transition material can beselected from any materials that undergo a phase transition at atemperature that is sufficiently low for the preservation of acryopreserved sample for a prolonged period of time, typically thistemperature is below the glass transition temperature of the sample, forexample a temperature of −70° C. or below. Preferably the phasetransition material is non-toxic and non-explosive thus avoiding anysafety concerns under standard operating conditions. Preferred examplesof phase transition materials are liquid to gas phase transitionmaterial such as liquid nitrogen which undergoes a liquid to gas phasetransition at −196° C., solid to gas phase transition materials such assolid carbon dioxide which undergoes a solid to gas transition at −80°C. and solid to liquid phase transition materials such as solid ethanolthat undergoes a solid to liquid phase transition at −114° C. In somecases, it is preferable to use a phase transition material that does nottransition into a gas as this avoids the need to provide venting of thegas that is generated by the phase transition. Reference to replacecartridges herein refer to the cartridge in its filled or empty state,i.e. to a cartridge containing cryogenic phase transition material orempty cartridges that can be charged with a cryogenic phase transitionmaterial.

Replaceable cartridges that are adapted to contain a phase transitionmaterial that undergoes a liquid to gas phase transition contain a ventto allow escape of gas generated during the phase transition, thus avoidthe risk of excessive pressure generation. Replaceable cartridges thatare adapted to contain a phase transition material that undergoes aliquid to gas phase transition may contain molecular sieves to absorbthe cryogenic phase transition material, this advantageously avoids therisk of liquid cryogen escape should the cartridge be punctured oropened in any way.

The replaceable cartridges can be disposable, i.e. single usecartridges, or can be recyclable, i.e. multiple use cartridges. Thereplaceable cartridges can be provided in a sterilised form to ensurecompatibility with use in operating theatres and other sensitiveenvironments. The replaceable cartridges can be provided in a cooledform, optionally in an aseptic package. In the case wherein thereplaceable cartridge is provided in an aseptic package the asepticpackage is preferably provided with venting means to avoid excessivepressure generation within the aseptic package.

The replaceable cartridge for receiving a phase transition material orcontaining a phase transition material can comprise a charging portallowing loading of the cartridge with phase transition cryogen materialsuch as solid CO₂ or liquid nitrogen. In some instances, the chargingport can be provided with a tamper proof seal. In some instances, thecharging port is sealed irreversibly after charging.

In one advantageous arrangement, the charging port can sealably engagewith a conduit provided in the housing for recharging of the cartridgewith cryogen, in which case the sealable engagement between conduit andcartridge avoids escape of the cryogen into the cavity. In thearrangement where the load of phase transition cryogen in the cartridgecan be recharged through a conduit in the housing, the conduit, i.e. therecharging conduit, is sealable to avoid unwanted escape of cryogenduring transit. Recharging of the cartridge in this arrangement can beeffected by engaging an external source of cryogen to a fitting, forexample a push fit fitting, on the housing at the end of the conduitdistal to the cartridge. Once the external cryogen source is engagedcontrol means located in the shipping container or in the cryogen sourcecan communicate with a fill sensor or temperature sensor in thecartridge allowing automatic recharging of the cartridge to theappropriate level. An exemplary external cryogen source would be a Dewarwith a control valve at its entry and a dip tube for immersion intoliquid cryogen at a first end and engagement with the recharging conduitof the shipping container at its other end. In operation the controlmeans can operate the control valve to deliver the liquid nitrogen intothe cartridge until a fill state sensor in the cartridge indicates thecartridge is full.

The replaceable cartridge can be made from any suitable material, forexample materials that can withstand the temperature at which the phasetransition of the cryogenic phase transition material undergoes phasetransitions. Exemplary materials from which the cartridge can be formedinclude plastics materials, for example polymer derived plasticsmaterials, ceramics and metals, including metal alloys.

It is preferable that the cartridge is provided with means forreleasable engagement within the cavity of the shipping container, forexample mechanical attachment means, for example a catch, lock or sliderarrangement that interact with a complementary element in, on or closeto the cartridge receptacle in the cavity. The attachment means can alsoform an electric contact between the cartridge and the container. Meansfor establishing electrical contact between the cartridge and theshipping container can be separate to any attachment means that may bepresent. The electrical contact can for example be used to confirm thepresence of the cartridge in the shipping container or to relayinformation on the temperature or fill status of the cartridge from asensor within, on or adjacent to the cartridge.

In some preferred cases the replaceable cartridge for receiving a phasetransition materials or containing a phase transition material may beprovided with one or more sensors configured to monitor the temperatureand/or fill state of the replaceable cartridge. In some examples, aplurality of thermocouples may be provided to allow the temperature atdifferent locations within the cartridge to be established. Theprovision of sensors to provide information on the temperature or fillstatus of the cartridge advantageous allows for user, local and/orremote monitoring of the temperature and/or fill state of the cartridgewithout opening the shipping container. These sensors can be located in,on or adjacent to the cartridge when it is located in the shippingcontainer. Information on the temperature or fill state of the cartridgemay also be relayed through a communication means, for example a wiredor wireless network, to trigger a further action. The fill state ortemperature may for example be indicated on a display on the containeror may be indicated on a remote device. Actions that are triggered bythe report on fill state or temperature may be the provision of aprompt, for example by e-mail or text message, to replace or rechargethe replaceable cartridge. Thus, in the instance wherein the containercomprises a Stirling cryocooler the report may be to report the need toactivate the Stirling cryocooler, to connect the container to externalpower or, if the container is connected to a power source power, toactivate Stirling cryocooler automatically. In one example theinformation on the fill state or temperature of the cartridge maytrigger despatch, for example by courier or other delivery means, of areplacement cartridge to the location in which the container is stored.In a further example the information could prompt the user to refill thecartridge with cryogen and could automatically despatch a refill vesselcontaining a cryogen for this purpose. In a further example theinformation provided by the sensor can indicate that the cryopreservedsample has been maintained under the set of conditions required tomaintained sample integrity during the shipping and storage process, forexample the tilt state, temperature history or the like.

The information on the fill state or temperature of the cartridge may besent in a continuous or periodic manner, the temperature status of thevessel over time can be monitored over time thus ensuring that theintegrity of the sample within the container is not compromised. Thiscan advantageously ensure that the sample storage history is logged andis verifiably in accordance with storage protocols, for example thoseset down to ensure that the sample is fit for use, for example that thesample is fit for clinical use.

The user replaceable cartridge may be provided with a handle tofacilitate handling of the cartridge. In some preferred examples whenthe replaceable phase transition material containing or receivingcartridge is located in the shipping container the cartridge handle hasa portion that is located at or towards the vertically uppermost portionof the thermal diode. This ensures that the cartridge can be withdrawnand replaced without exposing the user to extremely low temperatures. Toensure that any such handle does not cause excessive heat transfer tothe cartridge the handle should ideally be formed in narrow crosssection to minimise conduction to the phase transition material cryogen.

To provide for optimal performance in situations where the shippingcontainer is off-grid, i.e. where it is removed from external powersources, the shipping containers according to the invention may beprovided with an on-board power source, for example a battery such as arechargeable lithium ion, lithium polymer, nickel cadmium battery or anyother suitable conventional battery, suitable for driving the thermaldiode in the operational state wherein a heat pump, e.g. a Stirlingcryocooler, operates to provide active cooling to the cavity of theshipping container. The on-board power source will be selected asappropriate to the intended application. For example, for units that areintended for transit of samples between vehicles with an on-board powersource the unit it may only be necessary to power a heat pump such as aStirling cryocooler for up to and including one hour or two hours. Inother cases, for example where the shipper is to be used in air freightit may be desirable to incorporate an on-board power source thatprovides at least 24 hours autonomy to the shipper.

In addition to the on-board power source intended to drive the thermaldiode in the active state, in preferred embodiments the shippingcontainer is provided with an on-board power source to provide foroperation of communications means that report on the status of thesample or the conditions within the insulated housing of the shippingcontainer to a remote node. In some embodiments, the power sourceprovided for the communication means can be the same as that providedfor driving the heat pump. In some embodiments, the power sourceprovided for the communication means is separate to any power sourceprovided for driving the heat pump. It is preferred that a reserve ofpower for powering the communication means is provided so that if userintervention is required to ensure sample integrity is maintained analert can be sent from the container.

Practical considerations dictate that in use any sensor in thereplaceable cartridge, i.e. when installed in the shipping container, isin electrical communication with an electrical control element.Furthermore, effective electronic function in the control elementrequires that the operational temperature of the electrical controlelement is at a temperature above for example −140° C. since at lowtemperatures standard electronics will no longer function electrically,for example because there is a transition in the properties of otherwisesemi-conductor materials into electrical insulators at this point. Whenthe cartridge contains one or more sensors, the electronic controlelement that is in electrical communication with the sensor, for examplea thermocouple, is therefore positioned towards the vertically uppermostportion of the thermal diode or outside the cavity and may, for exampleby integrated into or attached to the side or top wall of the insulatedhousing or integrated to the handle element of the replaceablecartridge. It can therefore be understood that the control electronics,if present, are positioned in a region of the container that is warmrelative to the area in which the sample and cryogen reside.

The shipping containers according to the invention may also comprisemeans for performing a controlled rate freezing operation as describedin more detail below. As the person skilled in the art will be awarethere are a number of stresses that can be encountered during thecryopreservation process and these can be mitigated by controlling therate freezing. This is of particular interest as the shipping containersare of a suitable size to be used in an operating theatre environmentand could be used in such a context to cryopreserve samples, for exampletissue samples.

There are a number of options for controlled rate freezing. In a firstexample the temperature gradient inside the cavity of the shippingcontainer may be exploited to perform the controlled rate freezing. Inmore detail the temperature difference between the top of the cavity andthe bottom of the cavity is typically of the order of 100° C. A samplefor cryopreservation may be introduced into the top of the cavity andthen lowered into the cavity, for example on a platform, lift or by awinch arrangement. The rate of descent can be controlled by feedbackfrom a sensor, for example a thermocouple in, on or adjacent to thesample or sample holder. The rate of descent of the sample and thus itsfreezing rate can thus be performed according to a cooling algorithm todeliver a cryopreserved sample ready for despatch in its shippingcontainer. This approach is advantageously efficient in terms of phasetransition cryogen use as heat ingress into the system is minimised. Insome cases the cavity of the shipping container can be sealed with a lidonce the sample is inserted and active cooling to the cavity can beprovided with a Stirling engine. Power supply to the Stirling cryocoolercan be controlled by feedback from a sensor(s) located in the cavity oron the sample to match heat extraction from the cavity/cooling thereofto a predetermined cooling algorithm as appropriate to the nature of thesample and any medium in which it may be contained. These procedures canbe performed in reverse order, for example to conform with apredetermined warming algorithm, to allow a controlled thawing of thesample as a function of the ascent of a sample from the base of thecontainer or to the power delivered to a Stirling cryocooler driving thethermal diode. The practical means for performing controlledcryopreservation and thawing will be evident to those skilled in theart.

In a further example of how controlled rate freezing may be performedwith shipping container according to the invention the sample can beimmersed directly to the base of the cavity of the shipping container.In this case the sample holder or platform is equipped with atemperature sensor in, on or adjacent to the sample and a heatingelement. The temperature from the sensor is monitored and used tocontrol the heating. As with the previous example this configuration canbe used in reverse to allow a controlled rate thawing procedure, albeitin this instance this will involve depletion of the phase transitioncryogen.

In a yet further example of how controlled rate freezing may beperformed with a shipping container according to the invention a bed ofcooling beads can be provided at the base of the cavity. The sample canbe introduced directly into the bed of cooling beads. The rate ofcooling of the sample is controlled by the thermal contact between thesample and the cooling beads. The contact surface between the sample andthe cooling beads is in turn dictated by the size of the beads and thiscan be selected to deliver the desired rate of cooling.

The shipping containers as described herein that are adapted forcontrolled rate freezing can thus be used to generate cryopreservedsamples. For example, a tissue sample can be harvested and placed into abag containing a suitable cryopreservation medium that is sealed andthen introduced into the shipper unit for cryopreservation according toan automatic protocol as described above.

The shipping containers described herein and above provide a number ofadvantages over those containers presently in use. The combination of athermal diode arrangement and a replaceable cartridge of cryogenic phasetransition material allows for shipping and medium term storage ofcryopreserved samples in locations such as hospital and clinics wherecryogenic coolants are not routinely available. The shipping containercan serve as a storage container for a period of months when it arrivesat its destination. This long term cryopreservation can be achieved in anumber of modes. For example, mains electricity can be used to drive aStirling pump integrated or attached at destination or in transit to thethermal diode. Replacement of cooling cartridges can also be used forlong term storage, the despatch of cartridges to the container locationat its destination or in transit can be triggered by a report from thesensor in the container or the existing cartridge installed therein.Similarly, recharges of cryogenic phase transition material to be usedto recharge the cryogenic phase transition material in the cartridge orto drive the thermal diode in off grid locations, with despatch ofcryogenic recharges to destination being operable in an automatic mannerbased on report from the container to base thus prompting despatch ofthe appropriate recharge. In addition to this on-board power sources forpowering a heat pump can be provided in the container and these can berechargeable or replaceable to ensure continuous operation of the heatpump (e.g. Stirling cryocooler) when the shipping container is in anoff-grid location. Thus, as well as plugging in to a mains supply tomaintain cooling, a battery source, e.g. a rechargeable battery source,can be used to maintain active cooling while the shipping container isin transit.

The use of VIPs to form the insulated housing of the shipping containerrather than Dewars can be advantageous in certain circumstances. Theinventors of the present invention have discovered that temperatures ofaround −120° C. are effective for cryopreservation of cryogenicallypreserved samples for a period of months. Furthermore, for the reasonsdescribed above, namely that VIPs delivery a better thermal insulationof relative to standard Dewars in the temperature range of −60 to −100°C. cooling of the container by driving the thermal diode with a Stirlingcryocooler is more efficient with a VIP housing. This is economicallyadvantageous as a lower capacity Stirling cryocooler can be used todrive the Stirling engine. A combination of a Dewar vessel and VIPsadvantageously allows for a container with sufficient insulationproperties should the Dewar fail to maintain a cryopreserved sample inthe viable temperature range for user intervention and is of anacceptable weight for shipping.

The shipping containers of the present invention can also be used tocryopreserve biological samples via controlled freezing protocols asdescribed above. The physical size of the container means that thiscontrolled freezing can be performed in an operating theatre thusminimising the time at which samples are kept, and can degrade, atambient temperatures. The containers are also compatible with samplescryopreserved prior to introduction into the container. The need forcontainers as described herein is increasing as a function of thedevelopments in tissue regeneration/regenerative medicine, in cell basedtherapies as CAR T therapy and other therapies based on geneticallymodified tissues or cells.

There are a number of ways in which cryogenic shipping containers of theart and according to the invention could potentially fail as is shown inFIG. 5. For example, Dewar vessels are subject to cracking and loss ofvacuum that results in a rapid deterioration of the insulatingproperties of the Dewar vessel and a correspondingly small time windowin which a user can intervene to ensure that the integrity of acryopreserved vessel is not lost. The present inventors have developednew container structures that combine a Dewar vessel with a jacket ofvacuum insulated panels to provide an extended window for userintervention should such a failure occur and this, combined with theremote reporting functionality of shipping containers according to theinvention provides for a more robust system for dealing with potentialDewar failure. In cases where the Stirling pump operates via an on-boardpower source the provision of an internal cartridge of phase transitioncryogen material provides an extended window of opportunity to maintainthe integrity of a cryopreserved sample should the internal power sourcefail. Likewise, in cases where the Stirling pump fails the provision ofan internal cartridge of phase transition cryogen material provides anextended window of opportunity to maintain the integrity of acryopreserved sample. In each of these cases the failure will trigger analert to be sent to the remote server/node that can be relayed to theend user so that the end user can intervene to ensure that thecryopreserved material is saved. The alert can trigger despatch of theappropriate remedial means, for example despatch of a fresh shippingcontainer or cryogen or both simultaneously or sequentially.

In the instance where a communication unit failure occurs, the shippingcontainer can be provided with a backup, secondary, communication meansto ensure traceability and sample integrity. This can involve anautonomous GSM or satellite communication unit that reports on locationso that the last known position of the shipping container is storedremotely.

Condensed Gas as Working Fluid

In embodiments of the present techniques, a gas (such as air, oxygen,nitrogen, etc.) may be used as a working fluid within the shippingcontainer. As mentioned above, the working fluid is a means to provide atemperature gradient within the shipping container—the top of theshipping container (which, in use, is where a cooling mechanism isprovided) contains the warmest working fluid (which is to be cooleddown), and the bottom of the shipping container (which, in use, is wherea cryopreserved sample is located) contains the coolest working fluid.The build-up of condensed working fluid at, or near to, the bottom ofthe shipping container causes any relatively warm working fluid to flowup towards the top of the shipping container. During the above-describedsecond operational state of the shipping container, active cooling isapplied to enable heat to be extracted from the warm working fluid atthe top of the shipping container, and the cooled working fluid flowsdown towards the bottom of the shipping container.

The working fluid may be, or comprise, nitrogen gas, argon gas, air(e.g. from the environment in which the shipping container is provided),oxygen gas, or a liquified gas (e.g. liquified air). Liquid air is airthat has been cooled to very low temperatures such that it has condensedand become a liquid. Air (and liquid air) typically comprises nitrogen,oxygen, argon and other inert gases. Liquid air can absorb heat rapidlyand revert to its gaseous states. Thus, within the shipping container,the cool liquid air sinks towards the bottom of the shipping container,where it may assist in keeping a cryopreserved sample cold. The coolliquid air at the bottom of the shipping container may absorb heat,which may cause the warmed liquid air to rise towards the top of theshipping container and potentially revert to a gas state.

Using air, or liquified air, as the working fluid may be advantageousbecause a separate, dedicated supply of working fluid does not need tobe provided to the shipping container (e.g. a canister of liquidnitrogen). Instead, air from the environment surrounding the shippingcontainer may be input into the shipping container and cooled(condensed) to a cryogenic temperature. This may simplify the shippingcontainer design, and/or may lower operation costs.

FIG. 7 shows a graph of temperature change over time in a shippingcontainer during cooling and warming (bottom), and a graph of cryocoolerengine power over time during cooling and warming (top). The graphsrelate to tests performed on a shipping container to determine how theshipping container operates using condensed air and liquified air as aworking fluid. The tests were performed using a cryocooler (e.g. aStirling cryocooler) to cool air input into the shipping container. Athermal mass was placed at the bottom of the shipping container around acryopreserved sample in a sample bag. The thermal mass was 0.54 kg andformed of aluminium. For the purposes of the tests, at least, atemperature sensor is provided at two points on the thermal mass—one atthe bottom of the thermal mass (closest to the base of the shippingcontainer), and one at the top of the thermal mass (further away fromthe base of the shipping container)—to enable the temperature to bemeasured across the thermal mass, and across a height/length of thecryopreserved sample that is surrounded by the thermal mass. (Thermalmasses are described in more detail below with respect to FIG. 11).

When the cryocooler is turned-on and begins performing the function ofcooling down the air that is input into the shipping container, thepower consumed by the cryocooler rapidly increases, as shown in FIG. 7.The power consumed by the cryocooler is constant for a period 70, duringwhich time the cryocooler is working to cool down/condense the inputair. Thus, as indicated by arrow 74, the temperature of the cryocooler,as well as the thermal mass (top and bottom) and temperature of theshipping container decreases rapidly. During the period 70 when thepower consumption of the cryocooler is constant, air condensation takesplace—thus, as indicated by arrow 76, the temperature of the cryocooler,thermal mass and shipping container also becomes constant. Thetemperature reached at this stage is between −170° C. and −220° C., i.e.a temperature required to keep a cryopreserved sample cool. As shown inFIG. 7, there is a small difference in the temperature of the cryocoolerand the temperature of the thermal mass and shipping container.

Once the temperature required to keep a cryopreserved sample cool hasbeen reached by condensing the air to liquid air, the cryocooler isswitched-off and no power is consumed by the cryocooler, as shown inFIG. 7. The reduction in power is almost instantaneous. However, thecryocooler temperature does not increase instantaneously—arrow 78 showsthat the temperature of the cryocooler increases at a slightly slowerrate relative to the power consumption. The cryocooler itself is locatedat the top of the shipping container, i.e. at the opposite end of theshipping container relative to the cryopreserved sample. Thus, thetemperature of the cryocooler may increase relatively quickly comparedto the temperature of thermal mass and the bottom of the shippingcontainer. This is because any warmer air/warmer liquid air risestowards the top of the cryocooler and acts as an insulative layer thatprevents the heat of the shipping container from transferring to thebottom of the shipping container. Any warmer air/liquid air around thetop of the cryocooler functions as thermal insulation that keeps thecooler air/liquid air at the bottom of the shipping container. Thus, theduration 82 for which the liquid air remains cool and at the requiredtemperature is much longer (˜20 hours) than the duration for which thecryocooler remains cold.

Liquid air evaporation begins during duration 82, but takes place quiteslowly until enough liquid air has evaporated from the bottom of theshipping container that the thermal mass has started to warm-up.Duration 84 shows how the temperature of the thermal mass and bottom ofthe shipping container increases rapidly (by about 50° C. in a fewhours). At this point, the cryocooler is switched-on again and beginsconsuming power (as shown in FIG. 7), and as the temperature of thecryocooler decreases, the temperature of the thermal mass and bottom ofshipping container also decreases, as shown in FIG. 7. As thetemperature of the thermal mass and shipping container has not increasedto the original starting temperature, the cryocooler does not need tooperate for as long to decrease the temperature, and therefore, does notconsume power for as long as time as in the original condensation period70. However, as the cryocooler is powered-off fairly quickly and theactive cooling stage is shorter this time around, the thermal mass andshipping container begin heating-up quicker too, as shown by duration 86in FIG. 7. In the test, it was determined how quickly the thermal massand shipping container warm-up when active cooling is notapplied—duration 86 shows that the temperature of both increases by˜150° C. in around 15-20 hours when the cryocooler is not powered-on andactive cooling is not taking place. Arrow 88 shows the rate oftemperature decrease when the cryocooler is restarted and active coolingbegins again. This time, it takes a longer time for the thermal mass andbottom of the shipping container to cool down compared to the start(arrow 74). As shown at point 88, there is also a larger temperaturedifference between the temperature of the cryocooler and the temperatureof the thermal mass. This is because liquid air has not been produced bythe cryocooler during this active cooling period, i.e. condensation isnot taking place. As shown by arrow 72, less power is consumed by thecryocooler because no condensation is taking place.

FIG. 7 shows an advantage of providing a thermal mass around acryopreserved sample in a shipping container. The temperature datarecorded at the top of the thermal mass and the bottom of the thermalmass are very similar throughout the test period shown in the graph.Thus, the temperature across the cryopreserved sample will likely be thesame. This reduces the risk that, for example, the portion of thecryopreserved sample that is closer to the cryocooler/top of theshipping container warms-up at a different rate to the portion of thecryopreserved sample that is furthest away from the top of the shippingcontainer. If different portions of a cryopreserved sample are exposedto different temperatures, the viability of the sample as a whole may beadversely affected.

FIG. 7 shows that air (and liquified air) is an effective working fluid,and that the shipping container is capable of maintaining acryopreserved sample at a required temperature for a prolonged period oftime without applying power to the cryocooler. However, techniques tomaintain the required temperature when power is not applied to thecryocooler are also desirable—these are described in more detail below.Furthermore, problems may occur when the liquid air begins to warm-upand evaporate. The boiling point of liquid air is between the boilingpoints of liquid nitrogen and liquid oxygen. As a result, as the liquidair boils and evaporates (caused by absorbing heat at, or near to, thebottom of the shipping container), the nitrogen component evaporatesmore rapidly than the oxygen component of the liquid air. This mayresult in a liquid air mixture that contains up to approximately 50%concentration of oxygen. Liquid oxygen contains 4000 times more oxygenby volume than normal air, and materials that are usually considerednon-combustible (such as carbon, stainless steel, aluminium in powderedform, etc.) may burn in the presence of liquid oxygen. Many organicmaterials may react explosively with liquid oxygen. Accordingly, it isdesirable to reduce, minimise or eliminate the build-up of liquid oxygenwithin the shipping container.

Thus, in embodiments, there is provided a shipping container forcryopreserved biological samples, the shipping container comprising: aninsulated housing comprising a cavity for containing a cryopreservedbiological sample; and a thermal diode operable in a first state toprovide cooling to the cavity and in a second state to impair heattransfer into the cavity, the thermal diode comprising a gas.

FIG. 8 shows example steps performed by a system (e.g. a control system)to reduce build-up of liquid gas within a shipping container. Thecontrol system may be a dedicated control system specifically forreducing liquid oxygen build-up, or may be part of a larger controlsystem of the shipping container. (The control system may be part of aportable housing for the shipping container, such as the portablehousing described below in relation to FIG. 14A). The control system maycomprise at least two temperature sensors, one located at, or near to,the top of the shipping container, and one located at, or near to, thebottom of the shipping container. The temperature sensors may be locatedon an inner surface of the shipping container, and/or may be attached tocomponents within the shipping container, e.g. on the cryocooler, on thethermal mass, on a base of the shipping container, on a lid of theshipping container, between the cryocooler and the thermalmass/cryopreserved sample, etc. The control system may comprise morethan two temperature sensors. The control system may comprise additionalcomponents, such as comparators, processors, memory, user interfaces,controllers, etc.

For the sake of simplicity, the example steps shown in FIG. 8 are basedon a control system having at least two temperature sensors, one locatedat or near to the top of the cavity of the shipping container (i.e. nearthe cryocooler), and one located at or near to the bottom of the cavityof the shipping container (i.e. near the cryopreserved sample). Toreduce or minimise the build-up of liquid oxygen, the temperature withinthe cavity of the shipping container is monitored to determine if liquidoxygen has started to form. As mentioned above, liquid air comprisesliquid nitrogen and liquid oxygen, but as liquid nitrogen evaporates ata lower temperature than liquid oxygen, liquid air can end-up comprisinga higher concentration of liquid oxygen as the liquid nitrogen boils-offand evaporates. When the active cooling of the shippingcontainer/working fluid ends, the temperature within the shippingcontainer may remain at the temperature required to maintain acryopreserved sample for several hours to several days. Even if thetemperature at the top of the shipping container (T_(top)) increases, itis likely that the temperature at the bottom of the shipping container(T_(bottom)) will remain at the required temperature (or within adesired temperate range) for a long time due to a thermal air insulatingbarrier within the shipping container (as mentioned above with respectto FIG. 7). Thus, it is likely that a large temperature differencebetween T_(bottom) and T_(top) will exist while the bottom of theshipping container is at the required temperature. A reduction in thetemperature difference between T_(bottom) and T_(top) may indicate thatthe bottom of the shipping container is beginning to warm-up. This mayitself indicate that liquid nitrogen has boiled-off/evaporated, and thatthe amount of liquid oxygen in the shipping container may be increasing.The degree of closeness between T_(bottom) and T_(top) and the durationduring which the two temperature measurements are close, may indicatethat a substantial amount of liquid oxygen has formed in the shippingcontainer.

Accordingly, at step S100, the control system measures the temperatureT_(top) at the top of the shipping container, and at step S102, thecontrol system measures the temperature T_(bottom) at the bottom of theshipping container. It will be understood that steps S100 and S102 maybe performed in the opposite order or at substantially the same time. Atstep S104, the two measured temperatures T_(bottom) and T_(top) arecompared. If at step S106 T_(bottom) and T_(top) are determined to beclose, or if the difference between T_(bottom) and T_(top) is determinedto be within a specific range that indicates the temperatures are closeto each other, then the duration during which the temperatures remainclose to each other is monitored (step S108). If at step S106 themeasured temperatures are not determined to be close, the processreturns to step S100, as the difference between the measuredtemperatures is not indicative of liquid oxygen formation.

The duration for which the two measured temperatures remain close toeach other (or indeed, become closer), may indicate that liquid airformation has occurred (i.e. that liquid nitrogen has evaporated). Toreduce the amount of liquid air in the shipping container, it may bedesirable to heat the liquid air at the bottom of the shipping containerto cause it to evaporate into its gaseous state. However, a constantheat supply to the bottom of the shipping container is undesirable,particularly as this may cause the cryopreserved sample to warm up.Similarly, applying heat at regular, short intervals, may cause theshipping container to warm-up and may use a significant amount of power.It has been determined that to reduce the amount of liquid oxygen withinthe shipping container without increasing the temperature of theshipping container substantially or using much power, it is advantageousto wait a predetermined duration/period before applying heat to thebottom of the shipping container. Thus, at step S110, the control systemdetermines if the monitored time during which the two measuredtemperatures are close is approaching, or is equal to, a maximum timet_(max). The maximum time may be, for example, an a few minutes or a fewhours. The maximum time may be determined experimentally.

If the maximum time has been reached, the control system switches-on amechanism to reduce build-up of liquid air/liquid oxygen in the shippingcontainer (step S112). An example (heating) mechanism is described belowwith respect to FIGS. 9A to 9C. If the maximum time has not beenreached, the control system waits and returns to step S108.

The control system may, in embodiments, switch-off the heating mechanismautomatically after a specified time (e.g. after a few minutes), whenthe liquified gas is expected to have boiled-off. In embodiments, thecontrol system may determine when to switch-off the heating mechanism.To maintain the cool temperature of the shipping container (and maintainthe cryopreserved sample therein at the required temperature), it isvital to switch-off the heating mechanism to prevent the temperature inthe shipping container from increasing too much. In embodiments, thecontrol system may determine, using a resistive element provided withinthe heating mechanism (or elsewhere), if the liquified gas collected atthe bottom of the shipping container has substantially evaporatedaway/boiled-off. Thus, at step S114, the control system may measureresistance to determine if the resistance is indicative of the liquifiedgas having evaporated. (For example, if the resistive element, e.g. aresistor, is provided in a location where the liquified gas collects,the resistance may be low when the resistor is at least partly coveredby/surrounded by or in proximity to liquefied gas, while the resistancemay be high when the liquified gas has evaporated and the heatingmechanism is on.) At step S116, the control system may determine if themeasured resistance is equal to R_(max), which is indicative of therebeing substantially no liquified gas. If the measured resistance isindicative of there being substantially no liquified gas in proximity tothe resistive element, the control system switches-off the heatingmechanism (step S118) and the process returns to step S100. If themeasured resistance indicates some liquified gas remains within theshipping container, the control system returns to step S114. Inembodiments, the control system may automatically switch-off the heatingmechanism after a specific maximum duration, as a fail-safe in case theresistive element is faulty, to prevent the shipping container andcryopreserved sample from warming-up.

FIG. 9A shows a cross-sectional view through a shipping container 120comprising a mechanism to reduce build-up of liquified gas (e.g. liquidair) within the shipping container. The mechanism may be a heatingmechanism. The mechanism may be part of, or used in conjunction with,the control system described above with respect to FIG. 8. The shippingcontainer 120 comprises a thermal mass 122, which is provided in thevicinity of a cryopreserved sample (not shown). In embodiments, thethermal mass 122 may be shaped to at least partly contain or hold orsurround one or more cryopreserved samples. The heating mechanism toreduce build-up of liquified gas comprises one or more shallow vessels124 that are provided at the base of the shipping container 120. Thevessels 124 are provided at the lowest point (also referred to as a“sump”) in the shipping container 120 as this is likely to be thecoldest portion of the shipping container 120 and therefore, whereliquified gas will form or collect. The or each vessel 124 functions tohold liquified gas that forms within the shipping container 124. Inembodiments, a single shallow vessel 124 may be provided in the centreof the base of the shipping container 120. In embodiments, one or moreshallow vessels 124 may be provided at various positions on the base ofthe shipping container 120. FIG. 9B shows a plan view of one particulardesign of the mechanism to reduce build-up of liquified gas, whichcomprises four vessels 124 that are positioned around the edge/perimeterof the base of the shipping container 120 in an equidistant arrangement.

Liquified gas may be formed at the top of the shipping container, andmay drip down the shipping container. In embodiments, at least oneshallow vessel 124 may be provided on the base of the shipping containercavity in a location where liquified gas may drip (or be caused todrip).

FIG. 9C shows a cross-sectional view through a shallow vessel 124. Theshallow vessel 124 may comprise a sloped surface 126 (or bowl-shapedportion comprising a sloped surface) to cause any liquified gas whichfalls on the sloped surface 126 to flow into a recess 128. The recess128 may be within the bowl-shaped portion. The recess 128 may compriseor be coupled to a heating element (not shown) arranged to apply heat tothe recess 128 to evaporate the liquified gas within the recess 128. Theshallow vessel may comprise a resistive element 129, for the purpose ofdetermining when to switch-off the heating element, as described abovewith respect to FIG. 8.

In embodiments, the shipping container described herein may comprise amechanism to reduce a volume of liquified gas in the cavity of theshipping container.

The mechanism to reduce a volume of liquified gas in the cavity maycomprise: at least one vessel provided in the cavity to collectliquified gas; and a heating element to apply heat to the at least onevessel to evaporate the liquified gas collected in the vessel.

The vessel may, in embodiments, comprise: a shallow bowl-shaped portioncomprising a sloped surface; and a recess within the bowl-shaped portionfor collecting liquified gas.

In embodiments, the mechanism to reduce a volume of the liquified gas inthe cavity of the shipping container may comprise a controller forcontrolling when the heating element is to apply heat to the at leastone vessel. The mechanism may comprise at least one sensor in the recessof the vessel to sense when the vessel is empty, and wherein the atleast one sensor is coupled to the controller. The at least one sensormay be a resistive element provided in the recess of the vessel.

In embodiments, the shipping container may comprise at least one sensorto sense tipping or tilting of the shipping container. In embodiments,the at least one sensor may be provided as part of the shallow vesselfor collecting liquefied gas. The at least one tilt sensor to sensetilting of the shipping container may be coupled to the controller ofthe mechanism to reduce a volume of the liquified gas in the cavity ofthe shipping container. Wherever the at least one tilt sensor islocated, if the at least one tilt sensor senses that the shippingcontainer is tilted, the controller may prevent the heating element fromapplying heat to the at least one vessel. This may be useful because ifthe shipping container is tilted, the liquified gas may not havecollected within the vessel(s), and thus, applying heat to the vesselmay not result in evaporation of the liquified gas but may instead causeheating of the shipping container. This tip/tilt detection method mayalso be used to shut down the cryocooler to prevent the build-up ofliquified gas within the cavity of the shipping container. Inembodiments, if the least one tilt sensor senses that the shippingcontainer is tilted, and the container is in a liquification state, thenthe controller may prevent further liquification in the vessel.

In embodiments, the shipping container comprises a single vessel tocollect liquified gas, wherein the vessel is located in a base of thecavity. In alternative embodiments, the shipping container comprises aplurality of vessels in the cavity to collect liquified gas. Each vesselof the plurality of vessels may be coupled to a heating element. Thismay enable each vessel to be separately controlled to cause evaporationof any liquified gas in each vessel. This may be useful if the shippingcontainer is tilted, because only those vessels which are likely tocontain liquified gas (due to the angle of and/or degree the tilt), maybe heated to evaporate liquified gas.

FIG. 10A shows a cross-sectional view through a shipping containercomprising a mechanism to reduce build-up of liquid oxygen and frostwithin the shipping container, and FIG. 10B is a close-up view of themechanism.

FIG. 10A shows an airflow mechanism to enable gas to flow into thecavity of the shipping container 120 and to enable gas (e.g.evaporated—and therefore warm—liquified gas) to flow out of the cavity.The airflow mechanism may comprise a pipe 136 which is provided througha surface of the shipping container 120, e.g. through a lid or cover 134of the shipping container which seals an insulated housing 132 of theshipping container. FIG. 10A also shows a cryopreserved sample 130surrounded by a thermal mass 122 at the bottom of a cavity of theinsulated housing 132. A heat exchanger/heat sink/cool sink 146 is shownat the top of the cavity of the insulated housing 132. The cool sink 146is coupled to, or part of, a cryocooler to cool and condense gas whichflows into the cavity of the shipping container 120. The gas may be airfrom the environment in which the shipping container 120 is located. Thecool sink 146 may be surrounded by an insulating collar 150, which isdescribed in more detail below. The insulating collar 150 may be shapedto enable the pipe 136 of the airflow mechanism to extend into thecavity of the shipping container 120. In embodiments, input air may bedirected through a channel between the insulating collar 150 and theinsulated housing 132. When the input (warm) air flows into the spacebelow the cool sink 146, it may then flow upwards towards the cryocoolerand cool sink 146 where it can be condensed. This may be useful as itprevents warm air flowing directly towards the cryocooler and cool sink146. However, in embodiments, the pipe 136 may direct input air directlytowards the cryocooler and cool sink 146.

As shown in FIGS. 10A and 10B, a first part of the pipe 136 extends intothe cavity. A second part of the pipe extends out of the shippingcontainer 120. The second part of the pipe 136 is bifurcated or shapedinto a first branch and a second branch. An inlet is provided on thefirst branch of the second part of the pipe 136, to enable gas to flowinto the cavity of the shipping container 120. A one-way valve 138 isprovided along the first branch of pipe 136. This may prevent evaporatedair from within the shipping container to flow through the first branchof pipe 136, which may prevent the inlet from functioning correctly.

In embodiments, the first part of the pipe 136 extends into the cavityin proximity to the at least one cold finger or cryocooler or cool sink146. In embodiments, the first part of the pipe 136 extends into a topof the cavity (when the shipping container is in the use position).

The airflow mechanism comprises an outlet provided on the second branchof the second part of the pipe 136, to enable gas (including evaporatedliquified gas) to flow out of the cavity of the shipping container 120.A one-way valve 140 is provided along the second branch of the pipe 136.This may prevent gas from outside of the shipping container to flowthrough the second branch of pipe 136, which may prevent the outlet fromfunctioning correctly.

In embodiments, to reduce build-up of liquid oxygen within the shippingcontainer the airflow mechanism may comprise a chamber 142 locatedbetween the inlet and the one-way valve 138 on the first branch of pipe136. The chamber 142 may contain an oxygen scavenger. An oxygenscavenger, or oxygen absorber, is a material that helps to remove ordecrease the level of oxygen. The oxygen scavenger may be an iron-basedoxygen scavenger, or may be a non-ferrous oxygen scavenger. Thus, oxygenfrom the gas (e.g. air) that flows into the inlet of pipe 136 may be atleast partly removed, which reduces the potential build-up of liquidoxygen when the gas is condensed within the cavity of the shippingcontainer 120. In embodiments, the chamber 142 may be removably providedon the first branch of pipe 136. This may enable the entire chamber 142to be removed to enable the oxygen scavenger to be disposed of andreplaced with fresh oxygen scavenging material. In embodiments, theentire chamber 142 may be disposed of, and replaced with a new chamber142 containing fresh oxygen scavenging material. Additionally oralternatively, the chamber 142 may be openable in situ to enable theoxygen scavenger to be removed and replaced with fresh material.

In embodiments, to reduce build-up of frost within the shippingcontainer (particularly within the cavity of the insulated housing 132),the airflow mechanism may comprise a chamber 144 located on the firstbranch of pipe 136. If no chamber 142 is provided, the chamber 144 islocated between the inlet and the one-way valve 138 on the first branchof the pipe 136. If chamber 142 is also present, chamber 144 is locatedbetween chamber 142 and the one-way valve 138 on the first branch of thepipe 136, i.e. after the chamber containing the oxygen scavengingmaterial. Chamber 144 contains a desiccant or other suitable materialfor absorbing moisture/water from the input gas. Removing moisture/waterfrom the input air reduces the potential for frost or ice to form withinthe shipping container. Frost or ice may reduce the useable volumewithin the cavity of the insulated housing, may make it more difficultto place cryopreserved samples into the cavity or to remove them, andmay reduce the efficiency of the thermal diode of the shippingcontainer. For example, frost build-up on inner surfaces of theinsulated housing may block air flow channels/paths within the cavity,which may inhibit the correct functioning of the thermal diode/workingfluid.

In embodiments, the chamber 144 may be removably provided on the firstbranch of pipe 136. This may enable the entire chamber 144 to be removedto enable the desiccant to be disposed of and replaced with freshdesiccant. In embodiments, the entire chamber 144 may be disposed of,and replaced with a new chamber 144 containing fresh desiccant.Additionally or alternatively, the chamber 144 may be openable in situto enable the desiccant to be removed and replaced with fresh material.

In embodiments, the shipping container may comprise at least one getter.Turning to FIG. 13, this shows a cross-sectional view through a shippingcontainer 120 comprising at least one getter. A getter is a deposit of areactive material that is typically used to remove small amounts of gasfrom vacuum systems. When gas molecules (or liquid molecules) strike thegetter, the molecules combine with the getter chemically or byabsorption. The getter 170, 172, may be provided within the vacuumportion of the shipping container 120, as shown in FIG. 13. (Inembodiments, the getter may be provided within the cavity to absorbcondensed gases, or to absorb any liquified gas. The getter may alsohelp to reduce moisture within the cavity, which may otherwise result infrost build-up.)

In embodiments, the at least one getter may be provided in the insulatedhousing 132 of the shipping container 120. The at least one getter maybe provided as a coating on a surface of the cavity of the insulatedhousing 132. The at least one getter may be provided in proximity to thelocation of a cryopreserved biological sample 130 within the cavity,i.e. in or near to the coolest place within the cavity. Thus, getter 172is provided on, or near to, the base of the cavity of the insulatedhousing 132. The coolest place within the cavity may not always betowards the bottom/base of the cavity—at some points during thecryocooling process, the coolest place may be just above the location ofthe cryopreserved biological sample 130, e.g. when the coolest condensedgas has not yet reached the bottom of the cavity. Thus, getter 170 maybe provided in the insulated housing 132 at, or near to, the point wherethe top of the cryopreserved sample 130 will be located when the sampleis provided in the cavity.

Thus, in embodiments, the at least one getter is provided on, or nearto, a base of the cavity, and/or on a side wall of the cavity. Inembodiments, the at least one getter may be formed of charcoal. Inembodiments, more than one type of getter material may be used.

Maintaining Temperature of Cryopreserved Sample

As mentioned above, in the second operational state of the thermaldiode, in which no active cooling is provided (i.e. the cryocooler isswitched-off/powered-off), a temperature gradient between the top of thecavity of the shipping container and the bottom of the cavity of theshipping container (where the cryopreserved sample is located) ismaintained under gravity, as the coldest working fluid will reside atthe vertically lowest point in the cavity, and the warmest working fluidwill rise to the top of cavity. Once active cooling has been performed,it is desirable to maintain the cool/cold temperature within theshipping container (and therefore, of the cryopreserved sample) withouthaving to revert back to active cooling regularly. This is particularlyimportant when the shipping container is being shipped, and when activecooling may not be possible (because of safety requirements, or becauseof the lack of a power supply). If the temperature of the cavity of theshipping container increased rapidly, active cooling would have to beused regularly, which may also reduce the power-efficiency of theshipping container. Thus, techniques to maintain the temperature of thecavity, and cryopreserved sample, for as long as possible withoutperforming active cooling are now described.

In embodiments, a passive cooling technique may be used to maintain thecryopreserved sample at the required temperature for sample viability.FIG. 11A shows a cross-sectional view through a shipping container 120comprising a thermal mass 122 that surrounds a cryopreserved sample 130,wherein the thermal mass 122 is used to slow down the rate oftemperature change (increase) within the cavity of the shippingcontainer 120 (and more importantly, of the cryopreserved sample 130)when active cooling is not being used. The thermal mass 122 is a blockof material that is resistant to changes in temperature and therefore,stays cold for a long time after active cooling has ended. As shown inFIG. 11A, the thermal mass may be provided around the cryopreservedsample 130, to reduce the rate of temperature change in the vicinity ofthe cryopreserved sample. FIG. 11B shows a plan view of the thermalmass, and FIG. 110 shows a cross-sectional view of the thermal mass. Thethermal mass 122, or blocks/pieces of thermal mass, is arranged tosurround the cryopreserved sample 130. As the thermal mass 122 takes along time to heat-up after it has been cooled to a cryopreservationtemperature (e.g. −80° C. or lower), if the thermal mass 122 is providedclose to the cryopreserved sample 130, the cryopreserved sample isprevented from heating-up quickly. Thus, the thermal mass 122 providespassive cooling to the sample 130.

Thus, in embodiments, at least one block of thermal mass material isprovided in the cavity of the shipping container. Preferably, the atleast one block of thermal mass material is provided in proximity to acryopreserved biological sample in the shipping container. The or eachblock of thermal mass material may be shaped to surround thecryopreserved biological sample.

The or each block of thermal mass material may have a low thermalemissivity. The or each block thermal mass material may comprise atleast one surface having a low thermal emissivity. At least one surfacemay be a polished surface. The low thermal emissivity property means thethermal mass is poor at emitting thermal energy/thermal radiation.Consequently, the thermal mass 122 is able to keep the cryopreservedsample 130 cold, as thermal energy transfer between the thermal mass 122and the sample is reduced.

In embodiments, the or each block of thermal mass material may compriseone or more fluid channels to enable gas to flow through the block. Thismay improve the flow/circulation of gas through the cavity, i.e. cold,condensed gas may flow through the fluid channels to the bottom of thecavity, and warmer gas, or evaporated liquified gas, may flow throughthe fluid channels towards the top of the cavity where it can bere-condensed and/or may flow out of the cavity via the above-describedairflow mechanism. The fluid channels may advantageously prevent warmergas from collecting at the bottom of the cavity, where it could causethe cryopreserved sample 130 to warm-up.

The or each block of thermal mass material is formed of any materialsuitable for passive cooling, such as, but not limited to, aluminium,ice, or a phase change material. Typically, a material with a highthermal capacity may be suitable for the thermal mass.

The thermal mass(es) keep the cryopreserved sample cool (i.e. at therequired temperate for sample viability) for as long as possible whenactive cooling is not taking place. Another technique to maintain thetemperature of the cryopreserved sample is to minimise the amount ofthermal energy generated by the cryocooler that is transferred towardsthe bottom of the cavity and the cryopreserved sample.

FIG. 11A also shows a shield 158 in the shipping container 120. Acryopreserved sample 130 surrounded by a thermal mass 122 at the bottomof a cavity of the insulated housing 132. A heat exchanger/heatsink/cool sink 146 is shown at the top of the cavity of the insulatedhousing 132. The cool sink 146 is coupled to, or part of, a cryocoolerto cool and condense gas which flows into the cavity of the shippingcontainer 120. The gas may be air from the environment in which theshipping container 120 is located. The cool sink 146 may be surroundedby an insulating collar 150, which is described in more detail below.Shield 158 is provided in proximity to the cool sink 146 and cryocooler.Shield 158 may be an infra-red shield, to reflect thermal radiation uptowards the upper portion of the cavity or towards the cool sink 146,and away from the cryopreserved sample 130. The shield 158 may comprisea layer of insulating material 156 (e.g. a foam layer) that is coveredby a reflective material (e.g. aluminium foil). The shield 158 may becoupled to the insulating collar 150, via a hinge 160.

The shield 158 may be moved between a ‘closed position’ (as shown inFIG. 11A), in which the shield 158 acts as a barrier between thecryocooler and cool sink 146, and the cryopreserved sample 130, and an‘open position’, in which the shield 158 is moved out of the way so thatcooled gas may flow from the cryocooler towards the cryopreserved sample130. The direction of motion of the shield 158 is indicated by arrow162. The shield 158 may be coupled to a controller and mechanism toenable the shield 158 to be automatically moved between the closed andopen positions. In embodiments, the shield 158 may be controlled to moveinto the open position when the cryocooler is switched-on/is consumingpower, and the shield 158 may be controlled to move into the closedposition when the cryocooler is switched-off/is not consuming power.When the cryocooler is switched-off, the temperature of the cryocoolerincreases rapidly. When the shield 158 is in the closed position, theinsulating layer 156 prevents/reduces thermal energy transfer from thecryocooler to the cryopreserved sample 130, and the reflective surfacereflects thermal radiation away from the shield, insulating layer 156and cryopreserved sample 130.

Thus, in embodiments, an infra-red or thermal shield is provided betweenthe at least one heat (cool) sink and the cryopreserved biologicalsample, and is arranged to impair heat transfer from the heat (cool)sink towards the cryopreserved biological sample.

The shield may be moveable between a first position in which the shieldimpairs heat transfer from the heat sink, and a second position in whichthe shield enables the condensed air (and any liquid air) to flowtowards the cryopreserved biological sample.

The shield may be coupled to a control mechanism configured to: move theshield into the first position when the cryocooler is powered-off; andmove the shield into the second position when the cryocooler ispowered-on.

In embodiments, the shield 158 may be positioned in an intermediateposition (i.e. somewhere between the open and closed positions) tocontrol the dripping of any liquified gas towards the bottom of thecavity. For example, the shield 158 may be positioned in a positionduring active cooling which enables any liquified gas to drip downtowards one of the liquified gas collecting vessels described above withreference to FIGS. 9A-C. The shield 158 may be positioned in a positionduring active cooling which enables any liquified gas to drip away froma container for holding a cryopreserved sample within a shippingcontainer. For example, a container for holding a cryopreserved samplewithin a shipping container may be formed from a foam material (asdescribed below with reference to FIG. 18A). in this case, it isundesirable for liquified gas to drip onto the foam material, as it maybe absorbed by the foam. The foam-based container enables a user of theshipping container to easily remove the container and sample thereinfrom the shipping container, as the foam can be handled without glovesor specialist equipment. However, if the foam has absorbed the liquifiedgas, then when the foam-based container is handled by a user, skindamage may occur as the liquefied gas begins to evaporate. Thus, theintermediate position of the shield 158 may minimise or reduce theamount of liquified gas that drops onto the foam-based container. Thefoam-based container may be positioned within the cavity to reduce thepossibility of liquified gas falling onto the container, e.g. by beingrotated by 90° along the axis of the cavity, i.e. so that the foam-basedcontainer lies along the same axis as the shield 158 in the fully openposition.

As mentioned above, FIG. 11A shows a shipping container 120 having aninsulating collar 150. The insulating collar 150 may be coupled to, orpart of, the lid or seal 134 of the shipping container. The insulatingcollar 150 may help to maintain the temperature of the cryopreservedsample 130 at the required temperature when active cooling has ended.The insulating collar 150 may reduce or prevent any warm gas from theexternal environment from entering the cavity of the shipping container120, as the insulating collar 150 may function like a plug in thecavity. The insulating collar 150 may reduce thermal energy transferfrom the cryocooler when the cryocooler has powered-off after an activecooling stage, to the rest of the cavity, and in particular to thecryopreserved sample 130. The insulating collar 150 may help to keep thecooler air within the bottom of the cavity. The insulating collar 150may extend to the base of the cold sink 146, and/or be provided asmultiple collars that extend to the top of the thermal mass 122. Inthese embodiments, the collar may reduce thermal losses during transportcaused by the ‘sloshing’ of the cold air which result from the movementand tipping of the shipping container.

As mentioned earlier, the insulating collar 150 may be shaped to enableair to flow into the cavity for condensing when active cooling is takingplace. (The airflow mechanism described above may, in embodiments,function only when active cooling is taking place, and the inlet andoutlet may be blocked/closed when passive cooling is taking place. Inembodiments, the inlet and outlet may always be open, but airflow in andout of the system may be minimal when passive cooling is taking place).Thus, as shown in FIG. 11A, a gap or void 154 may be provided by theshape of insulating collar 150 to accommodate the pipe 136 of theairflow mechanism. A channel 152 may be provided from the gap 154 intothe cavity to enable airflow in and out of the airflow mechanism. Thechannel 152 may be provided by shaping the insulating collar 150 in away that it is not entirely flush to the cavity in a part of theinsulating collar, or by providing channel 152 in the insulating collar150.

Thus, in embodiments, the shipping container may comprise an insulatingcollar or plug. The insulating collar may be provided around the atleast one heat sink and/or cryocooler of the shipping container toimpair thermal energy transfer from the heat sink/cryocooler into thecavity during passive cooling (i.e. when the cryocooler is notoperational). The insulating collar may extend further into the cavitythan the at least one heat sink and/or cryocooler (as shown in FIG. 11A,for example). In embodiments, the shipping container comprises a lid forsealing the cavity, and the insulating collar may be coupled to, or partof, the lid, or may be separate from the lid.

In embodiments, the shipping container may comprise a thermal shield (asdescribed above). The shield may be coupled to the insulating collar andpositioned between the cryocooler and the cryopreserved biologicalsample, and be arranged to impair thermal energy transfer from thecryocooler towards the cryopreserved biological sample when thecryocooler is not operational (i.e. during the passive cooling state).The shield may be moveable between a first position in which the shieldimpairs thermal energy transfer from the cryocooler, and a secondposition in which the shield enables the condensed gas and liquified gasto flow towards the cryopreserved biological sample. The shield may becoupled to a control mechanism configured to: move the shield into thefirst position when the cryocooler is powered-off; and move the shieldinto the second position when the cryocooler is powered-on.

The insulating collar or plug may be formed of any suitable insulatingmaterial. In embodiments, the insulating material may extend downtowards the thermal mass in the shipping container cavity, when theinsulating collar/plug is inserted into the shipping container.Preferably, the insulating collar is formed from a material which offershigh thermal insulation per unit weight. As the lid and insulatingcollar need to be removed from the cavity when a cryopreserved sample isbeing stored in or removed from the shipping container, it is preferablethat the insulating collar is made from a relatively lightweightmaterial. In embodiments, the insulating collar may be fabricated from afoam material, such as, but not limited to a PVC foam or a closed cellPVC foam or an aerogel.

FIG. 12 shows a cross-sectional view through a shipping containercomprising a thermal mass 122 and an insulating collar 150. Duringpassive cooling, i.e. when the cryocooler 146 is switched-off, theabove-described properties of the thermal mass 122 and insulating collar150 enable a thermal gradient to form in the space 164 between thethermal mass and insulating collar 150. The warmest gas rises to the topof the space 164, and is prevented from flowing further up due to theinsulating collar 150. The coolest gas sinks towards the bottom of thespace 164, above/around the cryopreserved sample 130. During passivecooling, there is no significant gas circulation within the cavity, andthe stationary air functions as thermal insulation itself. In this way,the stationary air in space 164 helps to maintain the cryopreservedsample 130 at a required temperature.

Turning to FIG. 24A, this shows a heat sink 340 (or cool sink) of ashipping container. The cool sink 340 may help to cool gas whichcirculates within the shipping container during active cooling. The coolsink may increase the efficiency and/or speed at which gas within theshipping container is cooled by the cryocooler, by causing/encouragingconvective circulation of gas within the cavity of the shippingcontainer. The cool sink 340 is located at, or near to, the top of thecavity of the shipping container, in proximity to the cryocooler. Thecold sink 340 helps to draw warm gas within the cavity towards thecryocooler, where it can be cooled/condensed. The cold sink 340 maycomprise multiple fins. Preferably, the cold sink 340 comprises fansalong the length of the cold sink, to provide an improved convectivechimney effect. In embodiments, the cold sink may have a length ofbetween 50 mm and 300 mm, e.g. 150 mm. The length of the cold sink 340may depend on other design constraints of the shipping container (suchas the length of the cavity). The cold sink 340 may have a circularcross section—FIG. 24B shows a cross-sectional view (taken at line A′-B′in FIG. 24A) through an example heat sink having a circular form. Thecold sink 340 may have a rectangular cross section—FIG. 24C shows across-sectional view through an example heat sink having a rectangularform. As shown in FIGS. 24B and 24C, the cold sink 340 may have multiplefins 342, which increase the surface area of the cold sink 340, andtherefore, the efficiency of the cold sink 340. In embodiments, the coldsink 340 may have a fin spacing of approximately 5 mm. Thus, gas isdrawn through the void 344 and flows through/past the fins of the coldsink 340, which enables the cold sink 340 to cool the gas.

In embodiments, the shipping container comprises a cryocooler (e.g. aStirling cryocooler) to condense the gas of the thermal diode, whereinthe condensed gas provides cooling to the cavity.

The shipping container may comprise at least one cold finger coupled tothe cryocooler and extending into the cavity. The shipping container maycomprise at least one heat sink (cold sink) in proximity to the at leastone cold finger. The heat sink may surround the at least one coldfinger. The heat sink may function as an inverted chimney which drawsrelatively warm gas towards the at least one cold finger for cooling.The heat sink may have a larger surface area than a surface area of thecold finger.

The heat sink may be at least partly formed of copper. The heat sink maybe at least partly formed of aluminium.

FIGS. 21A to 21C show cross-sectional views through a shipping container120 having an insulating collar 300 and a sealing mechanism. FIG. 21Ashows a shipping container 120 comprising an insulating collar 300, suchas the insulating collar 300 described above. The insulating collar 300may be coupled to a thermal shield 304, such as the shield describedabove. The insulating collar 300 may be coupled to a lid of the shippingcontainer, or may provide the lid as shown in FIG. 21A. The void 302within the insulating collar 300 provides the space in which thecryocooler, cold finger, and heat sink may be provided. A gap 301 in theinsulating collar 300 in the lid portion may enable the cryocooler to becoupled to the engine which operates the cryocooler. A seal 306 isprovided between the lid portion of the insulating collar 300 and theinsulated housing of the shipping container, as shown. The seal 306 maybe provided by an O-ring in, or coupled to, the underside of the lidportion of the insulating collar 30. In embodiments, the seal 306 maybe, or may comprise, a foam material. The foam seal may be compressed,as shown in FIG. 21B. This is advantageous as if there is relativevertical movement between the engine and the cavity/insulated housing,the seal remains intact. The seal may need to be sufficiently thick suchthat it can be compressed down or can expand to fill a varying gapbetween the insulated housing and insulating collar 300. The seal mayalso remain intact if there is an angular misalignment between theengine and the cavity/insulated housing, as shown in FIG. 21C. Thismisalignment may occur if the shipping container experiences a shock, orif someone tries to twist apart the engine and the insulated housing.

A further technique for maintaining a temperature of the cryopreservedsample when active cooling is no longer taking place involves providingthe sample within an insulated container. FIG. 18A shows a container forholding a cryopreserved sample within a shipping container and formaintaining the sample at a required temperature when removed from theshipping container. It is important that a cryopreserved sample isthawed in a way that prevents ice formation within the sample, whichcould impact the viability of the sample. Thus, a specialised thawer maybe required to thaw the cryopreserved sample, which controls the rate ofchange of temperature. however, when a cryopreserved sample is removedfrom the shipping container, it will begin heating up quickly and in anuncontrolled manner. Thus, it is desirable to keep the cryopreservedsample at the temperature it was at in the shipping container when thesample is removed from the shipping container, for a few minutes. Thisallows the cryopreserved sample to be removed from the shippingcontainer and transferred to a thawer without the temperature of thesample increasing, or increasing too rapidly.

The container 280 shown in FIG. 18A comprises a foam skin and at leastone thermal mass within the container (not visible here). A void withinthe container provides a space for a cryopreserved sample. the containercomprises a plate (not visible) on which a cryopreserved sample 282 maybe placed. The container and cryopreserved sample 282 may be slottedinto the void of container 280. The plate comprises a handle 284 forhandling the plate, both when the plate is being inserted into the voidof container 280, and when the plate and cryopreserved sample areremoved and transferred to a thawer. This means a user does not have todirectly touch or handle the cryopreserved sample 282, which preventsheat transfer from the user to the sample. The thermal mass may becoupled to the foam skin in any suitable manner. However, as the thermalmass may expand and contract by a different amount compared to the foamskin, there may be limitations to the coupling technique. In thedepicted embodiment, the thermal mass is a layer/block of aluminium andthe block of aluminium is screwed to the foam skin using screws 286.Here, four screws 286 are used as this is sufficient to couple thealuminium layer to the foam skin while allowing the aluminium layer andfoam skin to expand and contract freely (and without the foam skincracking). The foam skin enables the whole of the container 280 to behandled by a user with their bare hands, and without specialistequipment, even when the temperature in the shipping container was −200°C. the handle 284 of the plate may also be covered in the foam materialfor similar reasons.

FIG. 18B shows how a cryopreserved sample 282 is inserted into andextracted from the container 280. The sample 282 is placed on plate 288,and plate 288 is inserted into (slides into) the void of the container280. The container 280 comprises two foam skins, which are each coupledto a thermal mass. The two foam skins are shaped in a manner such thatwhen the foam skins are brought into contact, a void is formed betweenthe foam skins. The foam skins comprise a plurality of magnets 292 tocouple together the two skins when brought into contact with each other,and to enable the container 280 to be quickly and easily disassembled(e.g. to extract a sample). the magnets 292 may be provided along edgesof the foam skins, as shown in FIG. 18B.

FIG. 18C shows the structure of the container 280 in more detail. Thecontainer 280 comprises a first foam skin 280 a and a second foam skin280 b. each foam skin 280 a and 280 b is coupled to a thermal mass 290,e.g. an aluminium block. The aluminium block 290 sits within a recesswithin a foam skin. A plurality of magnets 292 are provided around theedges of each foam skin 280 a, 280 b. one edge 291 of each foam skin 280a,b is shaped to enable the plate 288 to be slotted into the container280, and the edges 291 of the foam skins are aligned when the container280 is formed. Edges 291 define the top of the container 280. The bottomedge of each foam skin comprises at least one magnet 294. The magnet(s)294 magnetically engage with a magnetic element within the cavity of theshipping container, which is located within or on the base of thecavity. This enables the container 280 to be inserted into the shippingcontainer and positioned and held in a controlled, fixed manner withinthe shipping container. The bottom edge of each foam skin may comprise acut-away section 296, which may be used to enable a temperature sensorwithin the cavity of the shipping container to be coupled to at leastone of the aluminium blocks 290. This may enable the temperature of thealuminium block 290 to be measured in situ when the container andcryopreserved sample is within the shipping container. The temperatureof the aluminium block 290 will provide a good indication of thetemperature of the cryopreserved sample 282.

FIG. 19A shows a cross-sectional view through the container of FIG. 18A.The container 280 comprises a first foam skin 280 a and a second foamskin 280 b. Foam skins 280 a and 280 b are coupled to thermal masses 290a and 290 b, respectively. The shape of the foam skins 280 a and 280 bcreates a void when the skins are coupled together. This enables plate288 carrying the cryopreserved sample 282 to be inserted between thefoam skins.

FIG. 19B shows how a graph of the rate of temperature increase of acryopreserved sample and elements of the container of FIG. 18A when thecontainer is removed from the shipping container. As shown, thetemperature of the foam skins of the container increases very quicklyand by a large amount when the container is removed from the shippingcontainer. Here, the temperature of the foam skins increase by over 50°C. in under a minute, which is very fast and unsuitable for the thawingof a cryopreserved sample. in contrast, the temperature of the aluminiumblocks and the cryopreserved sample (bag top, bag middle, bag bottom)increases by only a few degrees in a minute. This shows that the thermalmasses of the container help to keep the cryopreserved sample cold evenwhen the container is removed from the shipping container. This providesa user with sufficient time (e.g. a few minutes) to extract thecontainer and transfer the container and sample to a thawer, withoutimpacting the viability of the sample.

FIG. 20A is another view of a foam skin of the container 280 which showstwo positioning magnets 294 in a bottom edge of the foam skin. Thepositioning magnet(s) 294 magnetically engage with a magnetic elementwithin the cavity of the shipping container, which is located within oron the base of the cavity. this enables the container 280 to be insertedinto the shipping container and positioned and held in a controlled,fixed manner within the shipping container. The bottom edge of each foamskin comprises a cut-away section 296, which may be used to enable atemperature sensor within the cavity of the shipping container to becoupled to at least one of the aluminium blocks 290.

FIG. 20B shows a view of the bottom edge of a container 280, and thecut-away section within foam skins 280 a, 280 b that enables theinsertion of at least one temperature sensor/probe into the container280. Just visible are the thermal masses 290 a, 290 b, which thetemperature probe(s) would contact to measure temperature and infer thetemperature of the cryopreserved sample.

Thus, in embodiments there is provided a container for holding at leastone cryopreserved biological sample within a shipping container of thetypes described herein.

The container may comprise: an outer insulating layer; a cavity withinthe container for at least one cryopreserved biological sample; and atleast one thermal mass provided as an inner layer, and coupled to atleast part of the outer insulating layer.

The container may comprise a pair of container halves adapted to beengaged together to form the container. Each container half of the pairof container halves may comprise an outer surface formed of aninsulating material, and an inner surface formed of a thermal mass. Thepair of container halves may engage together using a releasableengagement means. The releasable engagement means may be a magneticengagement means. Each container half may comprise a plurality ofmagnets.

The container may comprise at least one aperture. A temperature sensormay be coupleable to the container via the at least one aperture.

The container may comprise a docking mechanism for docking the containerinto a shipping container having a compatible docking mechanism. Thedocking mechanism may comprise at least one magnet.

The container may comprise a loading means for loading the at least onecryopreserved biological sample into the container. in embodiments, thismay take the form of a plate (as described above), which may be suitablefor samples in cryobags. In embodiments, this may take a form suitablefor samples provided in other types of containers, such as vials,multi-well plates, tubes, etc. in embodiments, more than one samplecontainer (e.g. cryobag, vial, multi-well plate, etc.) may be loadableinto a single container.

Portable Housing for a Shipping Container

FIG. 14A shows a perspective view of a portable housing 200 for housinga shipping container, the portable housing comprising an upper (top)portion 202, and a lower (bottom) portion 204. The portable housingcomprises a drawer mechanism which is slideably engaged with the lowerportion 204 of the portable housing. A shipping container 212 of thetype described herein is mountable in/couplable to the drawer mechanism.The portable housing 200 comprises a user interface or display 208 inthe upper portion 202. The portable housing 200 may comprise a handle211 or other mechanism to move the portable housing. The lower portion204 may comprise guide rails 214 or a similar mechanism to enable theshipping container 212 to slide in and out of the portable housing 200.The portable housing 200 may comprise wheels to help transport theportable housing 200, e.g. at positions 210 on the lower portion 204.The upper portion 202 may comprise at least one handle 206 for movingthe upper portion 202 into engagement with the lower portion 204 and fordisengaging the upper portion 202 from the lower portion 204.Preferably, two handles 206 are provided on opposite surfaces of theupper portion 206. The upper portion 202 may comprise at least theengine of the cryocooler. The lower portion 204 may comprise theinsulated housing.

When the upper portion 202 is engaged with the lower portion 204 (asshown in FIG. 14A), the drawer mechanism of portable housing 200 islocked, such that the shipping container 212 is locked within theportable housing 200. the portable housing 200 may comprise clasps orother locking mechanisms to retain the shipping container 212 in theportable housing 200. When the upper portion 202 is engaged with thelower portion 204, the engine is also coupled to the cryocooler of theshipping container and therefore, it is undesirable for the shippingcontainer 212 to be pulled out of the portable housing 200 as this maydamage the engine, housing and/or shipping container.

FIG. 14B shows a view of the portable housing with the upper portionraised. In this position, the upper portion 202 is disengaged from thelower portion 204, and the engine (not visible) is disengaged from thecryocooler in the shipping container 212. Part of the shipping container212 is located within the upper portion 202 when the upper portion 202is engaged with the lower portion. When the upper portion 202 isdisengaged, this part of the shipping container 212 is freed. A handle216 on the shipping container may be revealed, which can be used to pullthe shipping container 212 out using the drawer mechanism. FIG. 14Cshows a view of the portable housing with the upper portion raised andthe shipping container pulled-out. The lid/seal 218 of the shippingcontainer 212 is now visible—this can be removed to extract anycryopreserved sample within the shipping container 212 or to place asample within the container.

In embodiments, the shipping container 212 may not be fully extractablefrom the portable housing 200 by a user, to prevent damage to anyelectronics, circuitry, etc. which is provided between the shippingcontainer 212 and the portable housing 200. The portable housing 200 maybe returned by a user to a manufacturer/supplier for maintenancerequirements.

Not visible in FIGS. 14A-C is the means for coupling the portablehousing to a power supply (e.g. a mains supply), for the purpose ofpowering the engine and cryocooler. The portable housing may alsocomprise one or more batteries for a back-up power supply, to performlow-power tasks such as temperature sensing, or to maintain the display208 when mains power is disconnected. The portable housing may alsocomprise means for communicating with a remote server. This may be usedto provide information on the location of the portable housing 200, thestatus of the portable housing (e.g. temperature, remaining duration forwhich the cryopreservation temperature can be maintained, etc.) to aremote server/cloud service.

FIG. 15A shows a cross-sectional view of a mechanism to raise and lowerthe upper portion 202 of the portable housing 200 of FIG. 14A, with theupper portion 202 in a raised position. When the upper portion 202 is ina raised position, the upper portion 202 remains in the raised positionuntil a requisite amount of force is applied to lower the upper portion202. Resilient members 264 within the upper portion 202 and coupled tothe engine 268 cause the upper portion and engine 268 to move up to adatum surface 252. The resilient members 264 may be springs. Similarly,when the upper portion 202 is disengaged from the lower portion 204, theshipping container 212 moves up to datum surface 254 by means of theresilient members 262. The lower portion 204 comprises shock absorbers258 to protect the shipping container 212 from shocks imparted to theside of the portable housing. The lower portion comprises an end stop260 on the base of the lower portion 204 to protect the shippingcontainer 212 from hitting the base of the lower portion/portablehousing. The upper portion 202 comprises shock absorbers 258 to protectthe engine 268 from shocks imparted to the side of the upper portion202, and stops 266 to protect the engine from vertical shocks and toprevent the engine from moving any further. the shock absorbers 258, endstop 260 and stops 266 may be formed of rubber.

FIG. 15B shows the upper portion in a lowered position, and FIG. 15Cshows how the end stop 260 protects the shipping container 212. As theengine 268 and upper portion is lowered, the engine 268 makes contactwith the shipping container, and has sufficient load to push theshipping container down beyond its datum surface 254. As shown in FIG.15C, the shipping container 212 is pushed down against end stop 260. Theend stop, shock absorbers and stops 268 restrict movement of theshipping container and engine in all three planes. The spring rates ofthe resilient members 264 and forces required to lower the upper portionare chosen to enable the shipping container 212 to be pulled-up towardsthe datum surface 254 while remaining low enough for the engine 268 toovercome them to push the shipping container down towards the end stop260.

FIG. 16 shows a more detailed view of the portable housing 200 andmechanism of FIG. 15A. Here, guide rails 270 are visible. The upperportion 202 slides along guide rails 270, which enables the upperportion to be raised and lowered.

FIG. 17 shows a more detailed view of the upper portion of the portablehousing and mechanism of FIG. 15A. Here, the engine 268 is engaged withthe lid and insulating collar/foam plug 272 of the shipping container212.

Thus, in embodiments, there is provided a portable housing for theshipping container described herein. The portable housing may comprise atop portion; a bottom portion; and a drawer mechanism slideably engagedwith the bottom portion.

A shipping container of the type described herein may be mountable inthe drawer mechanism.

When the top portion is engaged with the bottom portion, the drawermechanism is locked within the bottom portion. When the top portion isdisengaged from the bottom portion, the drawer mechanism is able toslide within the bottom portion, to thereby enable access to theshipping container.

The portable housing may comprise at least one handle on the top portionfor raising and lowering the top portion.

The portable housing may comprise a user interface or display. The userinterface or display may be provided on the top portion.

The portable housing may comprise at least one tilt sensor to detecttilting of the portable housing.

The portable housing may comprise comprising a suspension system toabsorb shock during movement of the portable housing. The suspensionsystem may comprise one or more shock absorbers.

FIG. 22 shows an example user interface 208 of a portable housing for ashipping container. The user interface may be used to display anyinformation to a user of the portable housing. For example, the userinterface may display any one or more of:

-   -   a duration 320 indicating how long the shipping container may        remain at the required temperature when power has been        disconnected (i.e. during passive cooling);    -   a temperature 322 of the cavity of the shipping container (or of        the cryopreserved sample, as explained above);    -   an indication 322 of whether the portable housing has received        any shocks;    -   a tilt angle 328, indicating whether the shipping container is        tilted;    -   any alerts 330;    -   ambient/external temperature 332;    -   current time and/or date 334;    -   status information 324 (e.g. indicating whether the shipping        container is at a temperature suitable for inserting a        cryopreserved sample, or if the shipping container currently        contains a cryopreserved sample);    -   connectivity to a communication network for the purpose of        transmitting data to a remote server; and    -   a status of any liquified gas that maybe present in the shipping        container.

FIG. 23 shows a schematic diagram of example steps to determine how longa shipping container may remain at a required temperature when thecryocooler is switched-off. At step S500, a temperature sensor coupledto the thermal mass within the container for a cryopreserved sample (asdescribed above with respect to FIG. 18) is used to measure thetemperature of the thermal mass. The measured temperature is sent to aprocessor or controller (S502). The processor/controller receives thetemperature and compares the temperature to a temperature model (stepS504). Generally speaking, a thermal mass such as aluminium will warm-upat a linear rate. The temperature model used by the processor may begenerated from experiments conducted using the shipping container andbased on the same type and quantity of thermal mass in the shippingcontainer. the temperature model provides information on how long itwill take for the shipping container to warm-up when no active coolingis taking place. Thus, at step S506, the processor determines, using themodel and received temperature information, the time remaining beforethe cryocooler needs to be switched-on to prevent the temperature of thecryopreserved sample increasing to a point where the sample may startthawing. This may be range from minutes, to hours to several days. theremaining time is transmitted to a user interface (step S508) so that auser may determine if they need to take action to power-up thecryocooler. The processor may also transmit the remaining time to acommunication module (step S510) which may in turn transmit theinformation to a remote server (step S512). The measured temperature andremaining time may be stored by the processor and/or remote server, sothat it is possible to analyse the viability of the cryopreserved sampleat a later time.

FIG. 25 shows a flow diagram of example steps to safely park a Stirlingengine of a cryocooler. When a Stirling engine is suddenly disconnectedfrom a power supply (e.g. mains supply when the engine is being used foractive cooling), the engine may not park itself correctly, which coulddamage parts of the engine or cause parts of the engine to misalign. Toprevent damage to the engine or misalignment, it is useful to warn theStirling engine that power is to be disconnected, to allow the engineenough time to park itself. this may take a few seconds, e.g. 20seconds, i.e. is not instantaneous. When a mains power supply isdisconnected from the engine, or when the power supply is turned-off,the Stirling engine relies on at least one battery to keep running. Thebattery supply may always be connected to the Stirling engine duringactive cooling, so that it is ready to be used when mains power isswitched-off. The battery supply needs to be sufficient to enable theStirling engine to complete the parking process. Thus, the shippingcontainer and/or portable housing described above may comprise one ormore batteries for use in this parking process (as well as otherpurposes, such as keeping the user interface on, communicating with aremote server, temperature sensing and analysis to determine remainingtime at required temperature, etc.).

At step S600, a mains power supply to the engine is disconnected. Theengine now relies on one or more batteries for power (step S602). Acontroller/processor/circuitry may determine that mains power supply hasbeen turned-off and that the engine needs to safely park andswitched-off (step S604). The controller sends a control signal to theengine to park (step S606). Once the engine has parked, the batterysupply to the engine is disconnected so that the engine can bepowered-down (step S608).

Thus, in embodiments, there is provided a method for safelyswitching-off an engine of a cryocooler, the method comprising:determining a mains power supply has been disconnected from the engine;sending a control signal to the engine to park; and de-coupling theengine from at least one battery. The engine may be connected to the atleast one battery whenever the engine is connected to a mains powersupply.

The method may comprise determining that the engine has parked beforede-coupling the engine from the at least one battery. Alternatively, themethod may comprise waiting a specified period between sending thecontrol signal and de-coupling the engine from the at least one battery.the specified period may be approximately equal to or greater than atime required for the engine to park.

FIG. 26A shows a cross-sectional view through a shipping container 120and the location of liquified gas build-up within the container. Asexplained above, liquified gas may form at the top of the shippingcontainer, and may drip down the shipping container towards the base. Toachieve the lowest temperature at the base of the shipping containercavity, and to thereby achieve the longest standby time (i.e. the timeduring which active cooling is not taking place), the cryocooler mayneed to be operating such that the temperature of the cryocooler islower than the temperature of the shipping container base (as shown byarrow 76 in FIG. 7). Once liquified gas has been formed in the shippingcontainer 120, due to partial pressures, the nitrogen and air may havesubstantially the same condensation temperatures, such that theycondensate at similar rates. However, when the liquid nitrogenevaporates, the vapour within the shipping container may contain morenitrogen (e.g. ˜6% oxygen, ˜94% nitrogen). This mean that the liquid airthat builds-up in the shipping container base may contain more oxygen(e.g. ˜50% oxygen, ˜50% nitrogen). This means that the liquified airwhich builds-up in the shipping container base may essentially be 50%liquid oxygen, and the quantity of liquid oxygen may be a safetyconcern. Accordingly, it may be important to control the amount ofliquid oxygen that is present within the shipping container 120 at anytime.

In embodiments, at least one vessel 125 may be provided on the base ofthe shipping container cavity in a location where liquified gas may drip(or be caused to drip), as shown in FIG. 26A. In embodiments, theinternal surface of the shipping container may be shaped to provide avessel or recess within the surface of the cavity for collectingliquified gas.

The build-up of liquified gas may be controlled by, for example, warmingthe entire shipping container cavity to the boiling point of oxygen,such that the liquified oxygen is able to evaporate. However, thisresults in the whole system warming-up, which reduces the standby timeof shipping container 120. Furthermore, it may be difficult to quantifyhow much liquid oxygen is present within the shipping container, orpredict how much liquid oxygen may be likely to form within thecontainer. This may be a concern if the shipping container is used totransport cryopreserved samples by air, as air safety precautions mayrequire stating how much liquid oxygen is within the shipping container120. Similarly, the build-up of liquified gas may be controlled byoperating the cryocooler engine at a temperature range (e.g. −185° C. to−190° C.) that results in a minimal amount of liquified gas build-up.However, it may be difficult to control the operation of the engine suchthat it does not run at a much colder temperature, and as a result, itmay be difficult to quantify the volume of liquid oxygen in the shippingcontainer. Furthermore, if the engine does not run at temperatures thatresult in some liquid air build-up, then the temperature gradientbetween the top of the shipping container cavity and the base of theshipping container may be large enough such that coldest possibletemperature is achieved in the base of the shipping container.

FIG. 26B shows a cross-sectional view through a shipping container 120comprising a mechanism to reduce build-up of liquified gas (e.g. liquidoxygen) within the shipping container. This mechanism may help to solvethe above-described problem of not being able to control or quantify theamount of liquid oxygen present within the shipping container. Themechanism may be part of, or used in conjunction with, the controlsystem described above with respect to FIG. 8. FIG. 26B shows a shippingcontainer 120 comprising at least one cryopreserved sample 130. Theheating mechanism to reduce build-up of liquified gas comprises apumping mechanism to remove warm air from the top of the shippingcontainer cavity, heat the air to approximately room temperature (e.g.˜21° C.), and inject the heated air near the base of the shippingcontainer cavity. In embodiments, room temperature air from the externalenvironment may be used instead of, or in addition to, heating the airextracted from the shipping container. Injecting/pumping heated air nearthe base of the shipping container cavity, near the vessel 125 whichcollects the liquified gas, causes the temperature near the base of thecavity to increase, such that the liquified gas evaporates out of thevessel 125. In this way, the liquified gas volume in the shippingcontainer 120 may be reduced to keep the volume to acceptable, safelevels. This may be particularly important when the shipping containeris used to transport cryopreserved samples via air.

The pumping mechanism shown in FIG. 26B may comprise a pump 400, to pumpwarm air from the top of the shipping container cavity, heat the air toapproximately room temperature, and inject the heated air near the baseof the shipping container cavity. The pumping mechanism comprises afirst pipe 404 to direct warm air from the top of the shipping containercavity towards pump 400, and a second pipe 406 to direct heated airtowards the base of the shipping container cavity. First pipe 404comprises an inlet 404 a to draw air into pipe 404, and second pipe 406comprises an outlet 406 a to eject heated air towards the base of theshipping container cavity and in the vicinity of vessel 125. The pumpingmechanism may comprise a heat exchanger 402 between the pump 400 andoutlet 406 a, to heat the air pumped out of the shipping containercavity. In FIG. 26B, the first pipe 404 and second pipe 406 are shown topass through the lid or cover 134 of the shipping container 120. It willbe understood that FIG. 26B shows one example arrangement of thepipework of the pumping mechanism.

The pumping mechanism shown in FIG. 26B may have the advantage that thewhole shipping container cavity does not need to be heated to above 183°C. Furthermore, the pumping mechanism may be switched-on only whenliquified gas has collected in vessel 125, which may improve thepower-efficiency of the pumping mechanism and shipping container, andmay prevent heated air from being ejected into the shipping containercavity when liquified gas is not present. The pumping mechanism maycomprise a thermocouple, temperature sensor or similar device (notshown). The thermocouple may be located in vessel 125, or in or nearoutlet 406 a. When liquified gas has built up in the base of theshipping container 120, the thermocouple senses/measures a particulartemperature. When heated air is pumped into the base of the shippingcontainer 120 via second pipe 406, the thermocouple temperatureincreases when there is substantially no liquified gas in the vicinityof the thermocouple. Accordingly, the thermocouple may be used todetermine when liquified gas has collected in vessel 125, such that thepumping mechanism should be switched-on, and when liquified gas hasevaporated such that the pumping mechanism should be switched-off. Inembodiments, the thermocouple status may be evaluated regularly (e.g.every few minutes) to determine if liquified gas has collected or hasevaporated. This may prevent heated air from being ejected into theshipping container unnecessarily, which may prevent the overalltemperature in the container from increasing.

In the embodiment shown in FIG. 26B, the first pipe 404 and second pipe406 may be formed of a thermally insulative material, such as plastic.Thus, the pumping mechanism may not pose an electrical safety risk, andmay be readily sterilised. Additionally or alternatively, the mechanismto reduce the build-up of liquified gas in the shipping container maycomprise a resistive element that is coupled to the base of the shippingcontainer (e.g. to the vessel 125). For example, the resistive elementmay be one or more thin wires (e.g. copper wires) which heat-up when anelectrical current passes through the wires, and thereby heat theliquified gas. However, having electrical circuits in an oxygen-richenvironment may pose a safety risk. In embodiments, the pumpingmechanism and resistive element may be combined to reduce the build-upof liquified gas.

FIG. 27 shows a cross-sectional view through a shipping containercomprising a mechanism for sterilising the shipping container.Sterilisation may occur between shipping, i.e. when the shippingcontainer 120 is not being used to ship or contain cryopreservedsamples. The sterilisation mechanism may comprise a pump 400, tocirculate a vapour-based sterilant through the shipping container. Thus,the sterilisation mechanism comprises a first pipe 404 to draw gas fromwithin the shipping container cavity towards pump 400, and a second pipe406 to direct sterilant into the cavity. First pipe 404 comprises aninlet 404 a to draw gas into pipe 404, and second pipe 406 comprises anoutlet 406 a to eject sterilant and air back into the shippingcontainer. The pumping mechanism may comprise a sterilant source 502between the pump 400 and outlet 406 a. The sterilant may be any suitablematerial for sterilising the shipping container, and is preferably avapourised/gaseous sterilant. For example, the sterilant may bevapourised hydrogen peroxide, vapourised peracetic acid, or ethyleneoxide, though it will be understood these are merely non-limiting,illustrative example materials. In embodiments, the sterilisationmechanism may comprise a decontamination device system, such as Fogact(http://www.pharmabio.co.jp/en/clean-room-solutions/# fogact). Inembodiments, the sterilisation mechanism may comprise a UV light.

In FIG. 27, the first pipe 404 and second pipe 406 are shown to passthrough the lid or cover 134 of the shipping container 120. It will beunderstood that FIG. 27 shows one example arrangement of the pipework ofthe sterilisation mechanism. In embodiments, the lid 134 of the shippingcontainer 120 is placed on the shipping container when the sterilisationis taking place, which may reduce contact with any hazardous materialsduring the sterilisation, and ensures that the lid 134 is alsosterilised. Other elements usually present within the shipping container120, such as the thermal masses and sample holders, may be placed intothe shipping container 120 during the sterilisation process, or may beseparately sterilised.

In embodiments, the pipework of the pumping mechanism may be the same asthat of the sterilisation mechanism. This may simplify the design of theshipping container 120. The heat exchanger 402 and sterilant source 502may be swappable, so that the pump 400 can be used to either heat air orsterilise the shipping container. In embodiments, the pumping mechanismmay be used to heat the shipping container before the sterilisationmechanism is used to sterilise the shipping container 120. This may beuseful as warmer conditions may be required for the sterilant to workeffectively, and it may be faster to use the pumping mechanism to heatthe shipping container than to allow the shipping container to warm-upnaturally over time.

In embodiments, there is also provided a sensor for a shipping containerof the type described here, which may be configured to detect thepresence of absence of liquified gas in the shipping container usingtemperature profiles experienced during heating. For example, the sensormay use (or a controller coupled to the sensor may use) the rate ofchange of sensed temperature during different operation modes (i.e. ofthe cryocooler), to determine whether liquified gas is present withinthe cavity of the shipping container. As explained earlier, if thetemperature within the cavity of the shipping container changes tooslowly/quickly when, for example, the cryocooler is not in operation,this may be indicative of liquified gas being present in the cavity.

Embodiments of the present techniques also provide a non-transitory datacarrier carrying code which, when implemented on a processor, causes theprocessor to carry out the methods described herein.

The techniques further provide processor control code to implement theabove-described methods, for example on a general purpose computersystem or on a digital signal processor (DSP). The techniques alsoprovide a carrier carrying processor control code to, when running,implement any of the above methods, in particular on a non-transitorydata carrier or on a non-transitory computer-readable medium such as adisk, microprocessor, CD- or DVD-ROM, programmed memory such asread-only memory (firmware), or on a data carrier such as an optical orelectrical signal carrier. The code may be provided on a(non-transitory) carrier such as a disk, a microprocessor, CD- orDVD-ROM, programmed memory such as non-volatile memory (e.g. Flash) orread-only memory (firmware). Code (and/or data) to implement embodimentsof the techniques may comprise source, object or executable code in aconventional programming language (interpreted or compiled) such as C,or assembly code, code for setting up or controlling an ASIC(Application Specific Integrated Circuit) or FPGA (Field ProgrammableGate Array), or code for a hardware description language such asVerilog™ or VHDL (Very high speed integrated circuit HardwareDescription Language). As the skilled person will appreciate, such codeand/or data may be distributed between a plurality of coupled componentsin communication with one another. The techniques may comprise acontroller which includes a microprocessor, working memory and programmemory coupled to one or more of the components of the system.

Computer program code for carrying out operations for theabove-described techniques may be written in any combination of one ormore programming languages, including object oriented programminglanguages and conventional procedural programming languages. Codecomponents may be embodied as procedures, methods or the like, and maycomprise sub-components which may take the form of instructions orsequences of instructions at any of the levels of abstraction, from thedirect machine instructions of a native instruction set to high-levelcompiled or interpreted language constructs.

It will also be clear to one of skill in the art that all or part of alogical method according to the preferred embodiments of the presenttechniques may suitably be embodied in a logic apparatus comprisinglogic elements to perform the steps of the above-described methods, andthat such logic elements may comprise components such as logic gates in,for example a programmable logic array or application-specificintegrated circuit. Such a logic arrangement may further be embodied inenabling elements for temporarily or permanently establishing logicstructures in such an array or circuit using, for example, a virtualhardware descriptor language, which may be stored and transmitted usingfixed or transmittable carrier media.

In an embodiment, the present techniques may be realised in the form ofa data carrier having functional data thereon, said functional datacomprising functional computer data structures to, when loaded into acomputer system or network and operated upon thereby, enable saidcomputer system to perform all the steps of the above-described method.

Those skilled in the art will appreciate that while the foregoing hasdescribed what is considered to be the best mode and where appropriateother modes of performing present techniques, the present techniquesshould not be limited to the specific configurations and methodsdisclosed in this description of the preferred embodiment. Those skilledin the art will recognise that present techniques have a broad range ofapplications, and that the embodiments may take a wide range ofmodifications without departing from the any inventive concept asdefined in the appended claims.

1. A shipping container for cryopreserved biological samples, theshipping container comprising: an insulated housing comprising a cavityfor containing a cryopreserved biological sample; and a thermal diodeoperable in a first state to provide cooling to the cavity and in asecond state to impair heat transfer into the cavity.
 2. A shippingcontainer according to claim 1, wherein the cavity is suitable forreceiving a replaceable cartridge of cryogenic phase transition materialin addition to the cryopreserved biological sample, optionally whereinengagement means are provided for receiving a replaceable cartridge ofcryogenic phase transition material.
 3. A shipping container accordingto claim 1 or claim 2, wherein the thermal diode is a gravitationalthermal diode.
 4. A shipping container according to any preceding claim,wherein the thermal diode is capable of maintaining a temperaturedifference of up to 180° C. across its vertical height with a power lossof less than 10 W, for example less than 5 W or less than 3 W.
 5. Ashipping container according to any preceding claim, wherein the thermaldiode comprises an air blanket element or a closed circuitcondenser/evaporator loop element.
 6. A shipping container according toclaim 3 or claim 4, wherein the container comprises a heat exchangerconfigured to operate the thermal diode to provide cooling to thecavity.
 7. A shipping container according to claim 6 wherein the heatexchanger is located at the vertically uppermost portion of the cavitywhen the shipping container is in an upright position.
 8. A shippingcontainer according to claim 6 or claim 7 wherein the heat exchanger isthermally coupled to a heat engine.
 9. A shipping container according toclaim 6 or 7 wherein the heat exchanger is thermally coupled to areservoir for receiving a cryogen.
 10. A shipping container according toclaim 8 wherein the heat engine is a Stirling cryocooler.
 11. A shippingcontainer according to any of claims 6 to 10 wherein the heat exchangeris at least partially surrounded with an infra-red shield.
 12. Ashipping container according to any preceding claim, wherein theinsulated housing comprises vacuum insulated panels.
 13. A shippingcontainer according to claim 12, wherein the cavity is substantiallyrectangular in cross section.
 14. A shipping container according to anyof claims 1 to 11, wherein the insulated housing comprises a Dewarvessel.
 15. A shipping container according to any of claims 1 to 12,wherein the insulated housing comprises a Dewar vessel and one or morevacuum insulated panels.
 16. A shipping container according to claim 15,wherein the one or more vacuum insulated panels are located outside thecavity defined by the Dewar.
 17. A shipping container according to anypreceding claim, comprising one or more sensors for detecting thetemperature within the cavity or the temperature of a sample located inthe cavity, the location of the container, the power required tomaintain the temperature within the cavity stable, the amount ofcryogenic phase transition material in a cartridge located in thecavity, or the volume of a cryogen within the cavity.
 18. A shippingcontainer according to any preceding claim, comprising an electroniccontact for engagement with one or more sensors located within areplaceable cartridge of phase transition material.
 19. A shippingcontainer according to claim 17 or claim 18, comprising one or moresensors and a communication unit for reporting a reading from the one ormore sensors.
 20. A shipping container according to claim 19, whereinthe reading from the one or more sensors indicates the position of theshipping container, the temperature in the cavity, the heat loss fromthe cavity, orientation of the cavity, shocks and vibration that thecavity has been exposed to or the integrity of the sample or acombination of such parameters.
 21. A shipping container according toany preceding claim, comprising an insulated lid that is attachable tothe container to seal the cavity.
 22. A shipping container according toclaim 21, further comprising a lock, optionally wherein the lock isreleasable by remote control or by a remotely generated code, forexample in response to a signal verifying the integrity of thecryopreserved sample.
 23. A shipping container according to claim 21 orclaim 22, wherein the lid comprises a Stirling cryocooler configured toremove heat from the thermal diode or wherein the lid is adapted toreceive a Stirling cryocooler configured to remove heat from the thermaldiode.
 24. A shipping container according to any preceding claim,comprising means for controlled rate freezing.
 25. A shipping containeraccording to any preceding claim, comprising means for controlledthawing.
 26. A shipping container according to claim 24 wherein themeans for controlled rate freezing comprises means for controlling thedescent of a sample into the cavity in response to a reading from one ormore sensors located in the cavity or on the sample.
 27. A shippingcontainer according to claim 25 wherein the means for controlled ratethawing comprises means for controlling the ascent of a sample into thecavity in response to a reading from one or more sensors located in thecavity or on the sample.
 28. A shipping container according to anypreceding claim, comprising means for automatic extraction means forretrieving a cryopreserved sample and/or replaceable cartridge of phasetransition material from the cavity.
 29. A shipping container accordingto any preceding claim, comprising a conduit for fluid recharging of areplaceable cartridge of phase transition material located within thecavity of the container.
 30. A shipping container according to anypreceding claim, further comprising a replaceable cartridge forreceiving a cryogenic phase transition material.
 31. A shippingcontainer as claimed in any preceding claim wherein the thermal diode isoperable in a first state to provide cooling to the cavity using a gas,and in a second state to impair heat transfer into the cavity using agas.
 32. The shipping container as claimed in claim 31, furthercomprising: a cryocooler to condense the gas of the thermal diode,wherein the condensed gas provides cooling to the cavity.
 33. Theshipping container as claimed in claim 32 further comprising at leastone cold finger coupled to the cryocooler and extending into the cavity.34. The shipping container as claimed in claim 33 further comprising atleast one heat sink in proximity to the at least one cold finger. 35.The shipping container as claimed in claim 34 wherein the heat sinksurrounds the at least one cold finger and comprises a plurality of finsto absorb thermal energy from relatively warm gas that flows towards theat least one cold finger.
 36. The shipping container as claimed in claim35 wherein the heat sink has a larger surface area than a surface areaof the cold finger.
 37. The shipping container as claimed in claim 35 or36 wherein the plurality of fins are provided at least along a length ofthe heat sink.
 38. The shipping container as claimed in any one ofclaims 34 to 37 wherein the heat sink is at least partly formed ofcopper.
 39. The shipping container as claimed in any one of claims 34 to37 wherein the heat sink is at least partly formed of aluminium.
 40. Theshipping container as claimed in any one of claims 31 to 39 furthercomprising a mechanism to reduce a volume of liquified gas in thecavity.
 41. The shipping container as claimed in claim 40, wherein themechanism to reduce a volume of liquified gas in the cavity comprises:at least one vessel provided in the cavity to collect liquified gas; anda heating element to apply heat to the at least one vessel to evaporatethe liquified gas collected in the vessel.
 42. The shipping container asclaimed in claim 41 wherein the vessel comprises: a shallow bowl-shapedportion comprising a sloped surface; and a recess within the bowl-shapedportion for collecting liquified gas.
 43. The shipping container asclaimed in claim 42, wherein the mechanism comprises a controller forcontrolling when the heating element is to apply heat to the at leastone vessel.
 44. The shipping container as claimed in claim 43, whereinthe mechanism comprises at least one sensor in the recess of the vesselto sense when the vessel is empty, and wherein the at least one sensoris coupled to the controller.
 45. The shipping container as claimed inclaim 44, wherein the at least one sensor is a resistive elementprovided in the recess of the vessel.
 46. The shipping container asclaimed in any one of claims 31 to 45 further comprising at least onesensor to sense tipping or tilting of the shipping container.
 47. Theshipping container as claimed in any one of claims 43 to 45, furthercomprising at least one tilt sensor to sense tilting of the shippingcontainer, wherein the at least one tilt sensor is coupled to thecontroller.
 48. The shipping container as claimed in claim 47 wherein ifthe at least one tilt sensor senses that the shipping container istilted, the controller prevents the heating element from applying heatto the at least one vessel.
 49. The shipping container as claimed in anyone of claims 41 to 48 wherein the shipping container comprises a singlevessel to collect liquified gas, wherein the vessel is located in a baseof the cavity.
 50. The shipping container as claimed in any one ofclaims 41 to 48 wherein the shipping container comprises a plurality ofvessels in the cavity to collect liquified gas.
 51. The shippingcontainer as claimed in claim 50 wherein each vessel of the plurality ofvessels is coupled to a heating element.
 52. The shipping container asclaimed in any one of claims 31 to 51 further comprising an airflowmechanism to enable gas to flow into the cavity and to enable evaporatedgas to flow out of the cavity.
 53. The shipping container as claimed inclaim 52 where the airflow mechanism comprises: a pipe provided througha surface of the shipping container, wherein a first part of the pipeextends into the cavity and a second part of the pipe extends out of theshipping container, and wherein the second part of the pipe isbifurcated into a first branch and a second branch; an inlet provided onthe first branch of the second part of the pipe, to enable gaseous airto flow into the cavity; and a one-way valve provided along the firstbranch.
 54. The shipping container as claimed in claim 53 when dependenton claim 33, wherein the first part of the pipe extends into a topportion of the cavity.
 55. The shipping container as claimed in claim 53or 54 wherein the airflow mechanism comprises: an outlet provided on thesecond branch of the second part of the pipe, to enable gaseous air andevaporated liquid oxygen to flow out of the cavity; and a one-way valveprovided along the second branch.
 56. The shipping container as claimedin claim 53, 54 or 55 wherein the airflow mechanism comprises: a chamberlocated between the inlet and the one-way valve on the first branch, thechamber containing an oxygen scavenger.
 57. The shipping container asclaimed in claim 56 wherein the chamber is removably provided on thefirst branch.
 58. The shipping container as claimed in claim 56 whereinthe chamber is openable to enable the oxygen scavenger to be removed.59. The shipping container as claimed in any one of claims 56 to 58wherein the airflow mechanism comprises: a further chamber locatedbetween the chamber and the one-way valve on the first branch, thefurther chamber containing a desiccant.
 60. The shipping container asclaimed in claim 59 wherein the further chamber is removably provided onthe first branch.
 61. The shipping container as claimed in claim 59wherein the further chamber is openable to enable the desiccant to beremoved.
 62. The shipping container as claimed in any one of claims 31to 61 further comprising at least one block of thermal mass material inthe cavity.
 63. The shipping container as claimed in claim 62 whereinthe at least one block of thermal mass material is provided in proximityto the cryopreserved biological sample.
 64. The shipping container asclaimed in claim 63 wherein the or each block of thermal mass materialis shaped to surround the cryopreserved biological sample.
 65. Theshipping container as claimed in claim 64 wherein the or each block ofthermal mass material has a low thermal emissivity.
 66. The shippingcontainer as claimed in claim 64 wherein the or each block thermal massmaterial comprises at least one surface having a low thermal emissivity.67. The shipping container as claimed in claim 66, wherein the at leastone surface is a polished surface.
 68. The shipping container as claimedin any one of claims 62 to 67 wherein the or each block of thermal massmaterial comprises one or more fluid channels to enable gaseous airand/or liquid air to flow through the block.
 69. The shipping containeras claimed in any one of claims 62 to 68 wherein the or each block ofthermal mass material is formed of aluminium.
 70. The shipping containeras claimed in any one of claims 34 to 69, further comprising aninfra-red shield in the cavity.
 71. The shipping container as claimed inclaim 70 wherein the infra-red shield is provided between the at leastone heat sink and a position in the cavity for holding a cryopreservedbiological sample, and is arranged to impair heat transfer from the heatsink towards a cryopreserved biological sample.
 72. The shippingcontainer as claimed in claim 71 wherein the infra-red shield ismoveable between a first position in which the shield impairs heattransfer from the heat sink, and a second position in which the shieldenables the condensed gaseous air and liquid air to flow towards thecryopreserved biological sample.
 73. The shipping container as claimedin claim 72 wherein the infra-red shield is coupled to a controlmechanism configured to: move the shield into the first position whenthe cryocooler is powered-off; and move the shield into the secondposition when the cryocooler is powered-on.
 74. The shipping containeras claimed in any one of claims 33 to 69 further comprising aninsulating collar.
 75. The shipping container as claimed in claim 74wherein the insulating collar is provided around the at least one heatsink to impair heat transfer from the heat sink into the cavity.
 76. Theshipping container as claimed in claim 75 wherein the insulating collarextends further into the cavity than the at least one heat sink.
 77. Theshipping container as claimed in any of claims 74 to 76 wherein theshipping container comprises a lid for sealing the cavity, and theinsulating collar is coupled to the lid.
 78. The shipping container asclaimed in claim 77 wherein the lid comprises a resilient seal.
 79. Theshipping container as claimed in claim 78 wherein the resilient,flexible seal is at least partly formed of a foam material.
 80. Theshipping container as claimed in any one of claims 74 to 79 furthercomprising an infra-red shield in the cavity.
 81. The shipping containeras claimed in claim 80 wherein the infra-red shield is coupled to theinsulating collar and positioned between the heat sink and a position inthe cavity for a cryopreserved biological sample, and is arranged toimpair heat transfer from the heat sink towards the cryopreservedbiological sample.
 82. The shipping container as claimed in claim 81wherein the infra-red shield is moveable between a first position inwhich the shield impairs heat transfer from the heat sink, and a secondposition in which the shield enables the condensed gaseous air andliquid air to flow towards the cryopreserved biological sample.
 83. Theshipping container as claimed in claim 82 wherein the infra-red shieldis coupled to a control mechanism configured to: move the shield intothe first position when the cryocooler is powered-off; and move theshield into the second position when the cryocooler is powered-on. 84.The shipping container as claimed in any one of claims 74 to 83 whereinthe insulating collar is formed of a foam.
 85. The shipping container asclaimed in any one of claims 31 to 84 further comprising at least onegetter.
 86. The shipping container as claimed in claim 85 wherein the atleast one getter is provided in the insulated housing.
 87. The shippingcontainer as claimed in claim 85 wherein the at least one getter isprovided as a coating on a surface of the cavity.
 88. The shippingcontainer as claimed in any one of claims 85 to 87 wherein the at leastone getter is provided in proximity to a position in the cavity for acryopreserved biological sample.
 89. The shipping container as claimedin any one of claims 85 to 88 wherein the at least one getter isprovided on, or near to, a base of the cavity.
 90. The shippingcontainer as claimed in any one of claims 85 to 89 wherein the at leastone getter is provided on a side wall of the cavity.
 91. The shippingcontainer as claimed in any one of claims 85 to 90 wherein the at leastone getter comprises charcoal.
 92. The shipping container as claimed inany one of claims 31 to 91 further comprising a docking mechanism fordocking a container containing a cryopreserved sample within the cavity.93. The shipping container as claimed in claim 92 wherein the dockingmechanism comprises a magnet for magnetically docking the containerwithin the cavity.
 94. The shipping container as claimed in claim 92 or93 wherein the docking mechanism comprises at least one temperaturesensor couplable to the container when docked in the docking mechanism.95. A portable housing for the shipping container of any one of claims 1to
 94. 96. The portable housing as claimed in claim 95 comprising: anupper portion; a lower portion; and a drawer mechanism slideably engagedwith the lower portion.
 97. The portable housing as claimed in claim 96wherein a shipping container is mountable in the drawer mechanism. 98.The portable housing as claimed in claim 96 or 97 wherein, when theupper portion is engaged with the lower portion, the drawer mechanism islocked within the portable housing.
 99. The portable housing as claimedin claim 98 wherein, when the upper portion is disengaged from the lowerportion, the drawer mechanism is able to slide out of the lower portion.100. The portable housing as claimed in any one of claims 96 to 99further comprising at least one handle on the upper portion.
 101. Theportable housing as claimed in any one of claims 95 to 100 furthercomprising a user interface or display.
 102. The portable housing asclaimed in any one of claims 96 to 100 further comprising a userinterface or display on the upper portion.
 103. The portable housing asclaimed in any one of claims 95 to 102 further comprising a tilt sensorto detect tilting of the portable housing.
 104. The portable housing asclaimed in any one of claims 95 to 103 further comprising a suspensionsystem to absorb shock during movement of the portable housing.
 105. Theportable housing as claimed in claim 104 wherein the suspension systemcomprises one or more shock absorbers.
 106. A method for reducing avolume of liquid oxygen in a cavity of a shipping container forcryopreserved biological samples, the shipping container comprising afirst temperature sensor located near the top of the cavity, and asecond temperature sensor located near the bottom of the cavity, themethod comprising: measuring a first temperature at the top of thecavity; measuring a second temperature at the bottom of the cavity;determining a difference between the first temperature and the secondtemperature, wherein if the determined difference between the firsttemperature and the second temperature is within a specified range;switching on a heating mechanism to evaporate liquified gas in thecavity.
 107. The method as claimed in claim 106 further comprising:sensing when the liquified gas has been evaporated; and switching offthe heating mechanism.
 108. A method for safely switching-off an engineof a cryocooler, the method comprising: determining a mains power supplyhas been disconnected from the engine; sending a control signal to theengine to park; and de-coupling the engine from at least one battery.109. The method as claimed in claim 108 further comprising: determiningthat the engine has parked before de-coupling the engine from the atleast one battery.
 110. The method as claimed in claim 108 furthercomprising: waiting a specified period between sending the controlsignal and de-coupling the engine from the at least one battery. 111.The method as claimed in claim 110 wherein the specified period isapproximately equal to or greater than a time required for the engine topark.
 112. The method as claimed in any one of claims 108 to 111 whereinthe engine is connected to the at least one battery whenever the engineis connected to a mains power supply.
 113. A container for holding atleast one cryopreserved biological sample within a shipping containeraccording to any of claims 1 to
 94. 114. The container as claimed inclaim 113 comprising: an outer insulating layer; an cavity within thecontainer for at least one cryopreserved biological sample; and at leastone thermal mass provided as an inner layer, and coupled to at leastpart of the outer insulating layer.
 115. The container as claimed inclaim 113 comprising a pair of container halves adapted to be engagedtogether to form the container.
 116. The container as claimed in claim115 wherein each container half of the pair of container halvescomprises an outer surface formed of an insulating material, and aninner surface formed of a thermal mass.
 117. The container as claimed inclaim 115 or 116 wherein the pair of container halves are engagedtogether using a releasable engagement means.
 118. The container asclaimed in claim 117 wherein the releasable engagement means is amagnetic engagement means.
 119. The container as claimed in claim 118wherein each container half comprises a plurality of magnets.
 120. Thecontainer as claimed in any one of claims 113 to 119 comprising at leastone aperture.
 121. The container as claimed in claim 120 wherein atemperature sensor is coupleable to the container via the at least oneaperture.
 122. The container as claimed in any one of claims 113 to 121comprising a docking mechanism for docking the container into a shippingcontainer having a compatible docking mechanism.
 123. The container asclaimed in claim 122 wherein the docking mechanism comprises at leastone magnet.
 124. The container as claimed in any one of claims 113 to123 further comprising a loading means for loading the at least onecryopreserved biological sample into the container.
 125. A replaceablecartridge for receiving a cryogenic phase transition material for usewith a shipping container according to any one of claims 1 to
 94. 126. Acartridge according to claim 125 comprising a handle that extendstowards the top of the thermal diode when installed in a shippingcontainer according to any of claims 1 to
 94. 127. A cartridge accordingto claim 125 or 126, comprising one or more sensors for providinginformation on the fill state or temperature of the cartridge.
 128. Acartridge according to any of claims 125 to 127, provided with aconnector to form an electrical connection between one or more sensorsin the cartridge and control electronics for the one or more sensorslocated in a shipping container according to any of claims 1 to
 94. 129.The shipping container as claimed in claim 40, wherein the mechanism toreduce a volume of liquified gas in the cavity comprises: a pumpingmechanism to: extract air from the cavity, and pump room temperature airor heated air into the cavity.
 130. The shipping container as claimed inclaim 129 wherein the pumping mechanism comprises a heat exchanger toheat the air extracted from the cavity.
 131. The shipping container asclaimed in claim 129 or 130 wherein the pumping mechanism comprises anoutlet to direct heated air towards the volume of liquified gas in thecavity.
 132. The shipping container as claimed in any one of claims 129to 131 wherein the pumping mechanism comprises a sensor to determinewhen liquified gas is present within the cavity.
 133. A sterilisationmechanism for sterilising a shipping container according to any ofclaims 1 to 94 and 129 to
 132. 134. The sterilisation mechanism asclaimed in claim 133 wherein the sterilisation mechanism forces agaseous or vapourised sterilant into the shipping container.
 135. Thesterilisation mechanism as claimed in claim 134 wherein the gaseous orvapourised sterilant is any one of: vapourised hydrogen peroxide,vapourised peracetic acid, or ethylene oxide.
 136. The sterilisationmechanism as claimed in any one of claims 133 to 135, wherein thesterilisation mechanism comprises an ultraviolet light.